Over their decade long run, mobile 4X strategy games, sometimes known as SLGs, have brought in billions of dollars in revenue with only more to come.

For those wanting to get in on it, the history of these games is littered with both progress and mistakes that any hopeful successor would be wise to learn from. Their history may even foretell where the next generation of these games will go, and what the secret sauce of the next big one will be. You just need to know where to look.

Where am I coming from? Over the past nine years, I've played an array of 4X strategy games at a very hardcore level. Even as a player who doesn’t spend on IAPs, I’ve been the #1 player, led top clans, and sold my accounts for a tidy four figures. That’s the outside perspective I bring.

The inside perspective? I was the founding developer that led a team of engineers to build one such game, and was hands on for its conception, through prototyping, launch, and beyond. I can’t discuss internal numbers of course, but nothing’s stopping me from discussing external ones.

In the beginning, the strategy games in the appstores were quite light. Games such as Kingdoms at War succeeded in reaching the top grossing charts. These were forebearers to what I'd consider the first real 4X strategy games on mobile. They had buildings, and armies perhaps. You could fight and interact with other players, and there might've even been PvE. But there was no world map. No physical world the players resided in.

There were PC and web-games that had this to be sure, but those hadn't made the move to mobile, at least not yet.

There are far too many games in the genre for me to count let alone play to a deep enough degree. However, the seven I’ll go over paint an overall picture of the genre's history over a large time span, and will give us a perspective into what's worked, what hasn't, and what's to come. Let's get to it.

Kingdom Conquest

[November 2010]

This was the first game I played in this space. A lesser-known title from Sega which saw some decent success for its time, making it high into the top grossing charts. It had the prerequisites. Upgradeable buildings, ten levels each. Armies, themed as trading cards. Eye candy for UA in the form of 3D PvE encounters, though players quickly found out it was just a facade for a loot box. But most importantly, it had a world map, and the emergent behaviours that it brought to the table. Already a staple in the web-based games of the genre, this was one of the early implementations of world maps on mobile. It was a great game. I played the hell out of it. Unfortunately it had a fatal flaw that limited its lifespan and doomed it. More on that to come.

City Building in Kingdom Conquest

Eye candy, which didn't do much for gameplay, but helped with user acquisition

From the very start, this genre of games had a tight, addictive NUX. Quests guide the player’s actions. Return notifications call players back again and again. New mechanics are introduced keeping things interesting, and giving players milestones to strive for.

Kingdom Conquest's fatal flaw however was that they structured the game based on a short, finite season structure. After battling it out for multiple months, with a winner declared, player progress was reset. Not only this, but content was naturally structured with this in mind.

As many in the industry will know, the majority of the potential revenue from users comes from the tiny proportion of spenders who decide to spend a lot: the whales. To capture this full potential however requires time. Players can play for years and years, but artificially capping their lifespan slashes the full potential of this LTV.

As can be imagined, after a season reset, only a fraction of players return with the same interest and intent to spend. Any player would temper their spending in the game once they found out that even if they "won", it'd all be gone within a few months. Maybe it was a worthwhile experiment to try at the time, but it was a severe handicap in the end.

A brief lull in the genre followed until early 2012.

Kingdoms of Camelot: Battle for the North

[March 2012]

Here was the first mobile game in the genre that hit it big in this space. This was the mobile incarnation of what was already a Facebook success.

To the formula we had already seen in Kingdom Conquest, Kingdoms of Camelot added a few new things to the mobile mix. A distinct, though limited, research tree. Multiple player-owned cities. Simple heroes. Simple map PvE.

Building upgrades also included a minor twist, where players who wanted to fully upgrade the building to level 10 needed a premium item to do so. One which cost them premium currency, available through in app purchases.

However, despite the additional systems, the game proved to be less effective at monetization than future successors would be.

Their heroes, while a nice addition were simplistic and not fleshed out at all. Skipping the fine details about how they worked, players desired the benefits they provided, and would pay for them, but the shallow way they worked combined with the cost ceiling left a great deal of potential on the table. The limited research and useless PvE came with similar criticism. They were shallow and the game subsequently wasn't as effective at monetization as it could be.

The ability for players to own multiple cities was an interesting advent as a way to try to stretch out the content, something the web-based game also made use of. But really it wasn't necessary, as future takes on the genre would find: a single city with better-balanced building progression was cleaner, and better yet, was more conducive to monetization. Moreover, managing multiple cities was frankly tedious.

The emergent behaviours and PvP threats in the game world were also limited by a Kingdoms of Camelot-specific mechanic where players could opt to “hide” their troops, making them impervious to military losses. The resources in their city would be free for the taking in the meanwhile, but those were fairly easy to acquire. As a result, certain opportunities for conflict and the monetization that comes with it was lost altogether.

In an attempt to better monetize the game, part way through its lifespan the developers decided they'd allow troops to be directly purchased. Certain players loved this to be sure, and short-term revenues shot up as the ineffectively monetized players found an avenue to spend. But such an approach totally circumvented the rest of the game's content and balance. It was a tacked on lever that was completely disconnected from the rest of the game, with a high potential to break it, which it sure enough did. The game's leaderboards and community was subject to an inevitable p2w death spiral from which entire shards would never recover.

Imbalanced monetization resulting in unstable community and p2w death spiral (data from first shard)

As an aside, some of this data is available in part because of how easy it was to decompile Unity builds in the past, allowing enterprising individuals to bypass API security checks the game server had in place. One such individual used this information to build a site that periodically scraped game information, allowing players to do game-breaking things such as easily searching for player city locations on the map.

Despite its shortcomings Kingdoms of Camelot found success at the time as it stood above its rivals, and it would spin off skins such as The Hobbit: Kingdoms of Middle Earth.

The games that would follow it though made up for these shortcomings, with better fleshed out systems and deeper content to match. These successors would reap the benefits of far higher LTV ceilings as a result.

 Game of War

[July 2013]

Game of War offered a big step up. The simplistic systems of the previous generation were taken, and properly fleshed out, while weaknesses were shored up, and brand new competitive features added.

To start off, let’s go over the added depth. A hero avatar was introduced, with a fleshed out skill tree and equipment to match. Both the city and research content was now much deeper, offering a deeper progression path to both strive and monetize for. And the world map was now livelier, with more to observe and engage in. Player marches were now visualized, something absent in past iterations, resources could be gathered, and PvE was actually useful and rewarding. A player seeking more strategy in their games would find it here.

On the whole, the balancing seemed to have kept a better eye on player goals, and as a result they did a better job monetizing the critical path players take in the game as they build out their city and research the top tier troops. While in previous games an engaged player could pretty reasonably complete their city and attain top troops, it now took either considerable time and effort, or more likely, money, to achieve the same. Every successful game to follow would take a similar route.

All of these advancements together made for a deeper and more engaging game, which reaped far better LTVs.

To top it off, significant end game features were added, creating sources of conflict and goals for the biggest spenders. This came in the form of Wonders, a sort of clan-pvp king of the hill, along with shard vs. shard events, commonly referred to KvK. Both made use of added rallying mechanics, enabling the joint attack and defense of clan members and structures.

Wonders and Marches as implemented in Game of War

The basic formula laid out by Game of War would be carried forward in some form in all of the genre's successors to come. A new baseline had been set.

Outside of the game, Game of War was able to fully exploit its LTV advantages with tremendous UA efforts, including its infamous Kate Upton TV spots. Many in the industry questioned how they could be acquiring users profitably with the amount of spend here, but in the end, it's undoubtable how much of the market they captured as they had a solid position on the top grossing charts for a considerable stretch of time.

As time marched on though, cracks emerged. This was marked most significantly by the way live ops constantly pushed the economy and the game's players to the breaking point. Expensive whale content was frequently refreshed, which made older content obsolete, while at the same time aggressively inflating the economy.

It's impossible to say if this might've been the right move from an LTV standpoint. Their strategy was to aggressively suck out as much money as possible from players while they were still engaged, perhaps as a way to try to recoup their UA costs as soon as possible. What is clear though is that as this became more drastic, this was the specific thing that started to drive more players away, even their most dedicated whales. An informal survey of whales placed this as a top concern. Attempts to improve LTV may have backfired in the end.

Machine Zone, the makers of Game of War, would later try to run the same playbook with games like Mobile Strike and Final Fantasy XV, but a combination of a dated engine, mismatched expectations, and perhaps a change in the market limited the success of these endeavors.

 Clash of Kings / 

March of Empires

[June 2014 / August 2015]

The next major iteration on the genre came with the advent of clan-controlled territories on the map.

Games like Clash of Kings saw significant success here. Unfortunately this wasn't one of the games I chose to pick up during this period as I was deep in the game development grind. However, observing colleagues playing the game and reading up on the details it's clear it was a meaningful step forward and laid the ground for new sources of large scale organic conflict on the world map.

Here, clan members could work together to construct structures on the world map, which provided benefits and new capabilities to members within it.

Many games now have their own take on territory, and it's something that's still evolving. The game I did play during this time that tried to tackle territory in its own way was March of Empires, which saw only very limited success. Its take involved fixed territories and buildings on the map, as opposed to something more organic. Clans can take over these territories and buildings, which provide dwellers with advantages.

These different variations are perhaps a good example of some of the risks involved when exploring an untapped design space. While territory in Clash of Kings proved quite successful, the implementation in March of Empires felt lacking. It isn't sufficient to just try something new, you still have to get it right.

Regardless, territory mechanics were a meaningful advance forward, and something which various successors would continue to take up.

Lords Mobile

[February 2016]

Then came Lords Mobile.

The two most obvious steps forward were:

Casual friendly mechanic as seen in Lords Mobile..

.. with similarities to Heroes Charge and games of the like

This was built atop of what was now the standard fare of 4X features. The only major thing missing was clan territory functionality.

Beyond this, their hero system was further fleshed out to include a multitude of different heroes, each of whom could be leveled up. Some were premium heroes that could only be purchased, while others could only be attained from events. The game also benefited from a live ops team that ran a healthier economy than some of its predecessors, supporting player longevity.

From the outside I can only speculate, but considering players of these types of games can play and spend for years and years, this healthier player longevity could have resulted in a significant benefit to their LTV metrics in comparison to the short-sighted live ops mentality of the past.

Lords Mobile became a long-lived success, as evidenced by the hundreds of millions of downloads it racked up, more than any of its predecessors.

If there was any short-coming to point out, it might only be that it didn't push the fundamental gameplay forward that much. Someone who had played previous iterations wouldn't have had too much new to look forward to beyond the initial novelty from the grafted on casual mechanics. It achieved great success in spite of this however, perhaps a result of the expanded audience base it was able to reach.

 Rise of Kingdoms

[September 2018]

That leads to Rise of Kingdoms, which significantly pushed forward the real time strategy elements of the genre on mobile.

The strategy elements had grown stagnant on this front for many years, with developers just taking the old formula and adding some new bells and whistles. The addition of wonders and territory were notable, but were mostly just layered on elements atop of the same gameplay. Rise of Kingdoms would change this, carving out multiple new paths on this front.

For almost a decade now, the basic march functionality remained more or less the same. Players could send their armies from their city to a target, an attack would be resolved, and the army would return. That's it. Whether for technical reasons or lack of ambition, developers didn't invest in pushing this forward. The underlying world map mechanics remained the same across all of these previous games.

Rise of Kingdoms promotes their take as a combination of Real-Time Battles, and Unrestricted Troop Movement, but this doesn't do justice to spelling out all of the changes that were made to the underlying mechanics, and the strategy it enables.

Firstly, no longer are battles resolved instantly. Instead, when armies clash, combat plays out over a period of time, during which armies can withdraw, or reinforcements can arrive and change the outcome of the battle. This creates a more lively and dynamic environment, and a greater surface area for emergent behaviours to arise.

Amplifying this is what they market as unrestricted troop movement. Marches are no longer constrained to their simple: city-to-target, target-to-city routes. They can now be redirected mid-route, or halted altogether and ordered to camp out on the map. Moreover, marches can be intercepted mid-route. Combined, this enables whole swaths of new strategic behaviour. A single march for example can be sent out, hitting target after target across the map, causing mayhem. A band of invaders can coordinate their marches, invading and besieging enemy lands, locking inhabitants in. Conversely, since marches can now be attacked mid-route, no longer can an attack be launched deep into enemy territory with impunity. Geographic consequences come much more into play.

Speaking of that, there were advances on the map itself. In previous iterations, developers would take liberties as marches walked straight over water, mountains, and other cities unhindered. Here however, all of those create impediments that need to be navigated around. At its culmination, this creates natural choke points on the map which become focal points to be contested.

This enabling of time and space considerations allows for new dimensions of combat to be explored, and new ways to differentiate content. The time-factor for example enables heroes with a wide array of different abilities, damage over time effects, healing, buffs during certain health ranges, and more. Additionally the space-factor makes area of effect abilities possible, and makes troop speed a critical factor.

This is a far cry from the simple march mechanics of predecessors.

Significant gameplay advances in Rise of Kingdoms

Beyond this are other meaningful advances I won't dwell on. Massive zoom out capabilities, fog of war (though mostly cosmetic), an hour-long clan vs. clan battleground event with a heavy use of all of these new mechanics.

This sits atop of other tried and true pieces of the formula. Buildings, research, heroes, wonders, along with their particular take on territory systems and KvKs, where 8-shards compete over 2 months unlike most other games.

All told, if a new player were coming to the genre, or a hardened veteran was looking for the latest and greatest, Rise of Kingdoms would be the surefire game to point them to.

From the UA perspective, the game was originally titled Rise of Civilizations, later renamed due to trademark disputes. It's reasonable to speculate they may have been looking to benefit from organic searches for Sid Meier's seminal game. It also seems like it may have been a conscious choice to attempt to reap the worldwide UA benefits of the free "IP" available by centering the game around different nationalities and historical figures. The appeals of a Joan of Arc, Caesar, Cleopatra, or Sun Tzu.

Cleopatra and other historical figures potentially aiding UA

A Deeper Dive

From the game design perspective, there are three specifics worth calling out that play a significant part in shaping the actual gameplay as well as the monetization. These are the sort of things that might be easily overlooked unless you were a longtime player of the game.

First, a combination of the design decisions and the emergent behaviours that play out results in an environment that can be significantly more survivable and forgiving for a larger number of players, keeping them in the game longer. For example, the hospital and troop death rules are laid out in a way where combat can be much more forgiving in lower stake scenarios, while also being more risky for would be aggressors. Combined with the ability to intercept marches mid-route, this reduces situations where large players will want to take the risk and pay the cost of picking on weaker players - a frequent complaint in games of this genre. "Zeroings", where players lose all their troops, can still happen but are much rarer. To top it off, the need for cooperation to succeed in KvKs creates a strong incentive for shards to coalesce, and as a result after an initial period of conflict, most successful shards find ways to organize and work together peacefully, with the only major conflict occurring in KvKs. With time, this practically eliminates such zeroings outside of KvKs, and with it the sort of harassment that makes a lot of players quit early on.

Second, monetization seems very healthy up front. With some meticulous data collection, and using information they happen to make available in the game, it's possible to get a detailed assessment of certain player spending habits. Without going into fine details, the rate of monetization during my assessment period was very strong, a multiple over a less successful competitor at the time. For whales, a large part of this seemed to go towards acquiring limited hero content, where certain heroes were structured in a way that they could only be acquired by competing over them in events. This is on top of the desire to spend on other forms of content, especially research and troops, with an added boost of revenue during seasonal events.

To provide a little peek into the data collected, here was the spending behaviour from the top clan in one of the top shards over a one month period.

Daily spend by bundle type, heavily driven by event competition and content

80% of revenue came from players who spent $1000+ in one month

At the same time, the monetization balancing is far more f2p friendly, in that monetizing players get less of an advantage for their money than they do in competing games. Eyeballing it at one point, I found that a $10 bundle gave about 4x more of an advantage in Lords Mobile than in Rise of Kingdoms. As a result, f2p players aren't as ridiculously outgunned, and monetizing players also need to pay more for the advantages they desire. Furthermore, as is the case in many of these games, when someone purchases certain bundles, their clan mates benefit by getting a gift of beneficial items or speedups. The final balancing is such that if you're able to make it into the top clan in your shard, you can benefit tremendously to the point where even as a f2p player it's possible to unlock all of the main pieces of content aside from the heroes. This is something that would cost players thousands of dollars to unlock in a reasonable timeframe otherwise.

To provide an anecdote to give you a sense of this, even though I play these games quite dedicatedly, I never buy IAPs. In less than a year, I was able to unlock the top tier of troops, and sell my account for a low 4-figures when I left the game. This amount isn't something that was feasible in the balancing of other games.

The other side of this though is the cost to the developers. If someone who doesn't buy IAPs is able to unlock top tier troops in that time frame, players who do monetize can do so even sooner, cutting off one of the primary drivers for monetization earlier on than in other games. Other reasons to continue monetizing remain, but these aren't as enticing as completing your research and unlocking the top tier troops. I could imagine this putting a meaningful dent in their non-whale LTVs. Inadvertently, it's possible this helps create a fiercer, more competitive environment for whales to continue spending against. Considering they make up 80%+ of the revenue, perhaps this is a worthwhile trade off.

The third thing worth calling out involves the consequences of the peaceful in-shard metagame, in contrast with the 2-month long KvKs. The KvKs can be intense, and prove a great incentive for players to monetize, at least the first time players participate in them. Due to their intensity however, the consequences and potential losses can be equally large. While it doesn't happen in every KvK, once players have a sense of the costs involved, if the leaders of a shard get the sense they won't have an easy time and be able to sweep the KvK, there will be strong incentives to reach a diplomatic end to the KvK, and divvy up the rewards. Similar to what happens in individual shards.

This has related knock-on effects. If KvKs typically reach a quick diplomatic end, entire shards will lose their last remaining source of conflict, not a great result. At the same time, if KvKs don't wind up this way, KvKs are just too intense to be run too often. The result being that after the heightened activity of a KvK, players return back to their home shards for months worth of peace. It's quite anti-climactic, and I can only imagine it hurting their daily revenue numbers. The coming and going of conflict for large periods of time also seems non-ideal when it comes to encouraging regular player spending habits. A long break from conflict-driven reasons to monetize seems to provide players a good excuse to break their IAP addictions, or even leave the game altogether.

Though these issues may limit its full potential, Rise of Kingdoms is undoubtedly a sizable step forward for this genre on mobile.

What's Next?

Mobile 4X strategy games have thrived for a decade now, and will continue to do so for years and years to come. They've undergone a constant evolution to get to where they are now, continuing to set higher and higher gameplay bars, and higher and higher metrics.

It'd only be fair to ask, "What's next?"

In my previous life as a game developer, I've predicted and pushed for some of the very elements that have come to see breakthrough success in this genre. Not all of them certainly, but if you know where to look a certain pattern emerges, much of it in plain sight.

On the gameplay side, players who crave strategy will want more and more strategy. In many ways in this genre, mobile is playing catch up with PC games. When you look at something like the original Warcraft, or even games that preceded it, the gameplay there already delivered what's only now at the cutting edge of the actual strategic gameplay on mobile. Specifically, unrestricted troop movement and real-time battles only came in 2018, over 20 years after Warcraft. On the technical front these are much more challenging to deliver in a massively multiplayer online game, so it's no wonder it's taken awhile to get here, but as developers continue to push on to try to deliver the next top grossing hit, these elements will continue to find ways to mobile.

So as a player, or a developer who's asking what'll capture player imaginations next, the answers are already out there.

Things like airborne troops common in RTSes open up swathes of strategy. Instead of just the surface-to-surface troops of today, we now have surface-to-air troops, air-to-surface, air-to-air, surface-to-all, or air-to-all attack types. Congratulations, you've just exploded the interesting combinations, content, and strategy you can deliver.

Or even changing some of the fundamentals, and moving towards more of a Civilization-like approach, where units on the map move slowly and gradually in more of a real-time fashion, and freedom of opposing troops on the map can be completely restricted and blockaded. This would open up problems to be solved to be sure, but it delivers on totally new strategy and gameplay.

There are numerous promising avenues here, both in and outside RTSes. Territory systems for example long existed in MMORPGs before RTSes.

Capital ships. WMD attacks. Shardless game servers. Troop transportation units. Espionage. And I'm sure plenty more come to your mind when you think about the possibilities.

To those wanting to deliver on strategy, the investment needed to develop these games will grow ever higher. It'll be harder and harder for smaller developers to fund a team that can build this out. And the teams that can be funded will require costly bets.

For those who love these games though, the years to come should only bring more of what you love. And to those with the foresight to deliver on it will come the spoils.