Game Breaker / Imperator: Rome

• Military colonies. If a country can have them, any army that has at least 10 cohorts in it can settle any given province that has less than 5 pops, adding freemen pops (the one responsible for manpower) out of thin air. In practical terms, it means you can generate population out from a vacuum, as long as you don't mind extensive micromanagement. And if the province in question has slave pops, you can relocate it and then settle it with some more soldiers. It is particularly potent when building a new city in a sparsely populated province or when Settling the Frontier of freshly conquered territory with a loyal population of your own culture and religion.
  • This was eventually balanced by having the provincial loyalty decrease by 15 per freeman pop added. ^note Players lose control of provinces (can't build buildings, move slaves etc) when provincial loyalty drops below 33; you also cannot add freemen pops via military colonies once provincial loyalty drops below 33. When it reaches 0, the province outright rebels. In addition, the perk itself is restricted to cultures who can access Greek, Persian and Levantine traditions. It's still very powerful for those who can use it.
• Slave raid. On paper, it incurs Aggressive Expansion penalties that aren't worth it, 1 point per 1 pop snatched. In reality, they can neuter completely Early Game Hell for any minor country or a city-state, since you can quickly double or triple the size of your starting economy, while simultaneously bleeding your targets of population. Once you have the ball rolling with slave-backed economy, that AE turns into being just a number. After establishing yourself as a regional power, there is nothing preventing you from just farming globally, simply set up footholds at fringes of your existing naval range. Considering how often you can raid for slaves and how slow the natural population growth is, it is possible to depopulate entire shorelines in some backwater regions. Amoral? The game encourages it, especially against targets that won't be conquered by you within the next century or so.
  • Raids can be conducted on countries you have a truce with. The target can't do a thing about it, while you farm them dry.
  • Target ports got fortified? Bring bigger ships and not only continue the raid as if nothing, but destroy - without declaring war or any direct diplomatic damage - a fort for easier conquest a few years/months/days later.
  • Not to mention there are situations where having high Aggressive Expansion is desirable and nothing raises it as fast as raiding for slaves.
  • Eventually, slave raids were nerfed by restricting its availability to cultures who have unlocked Greek or Indian traditions, and the tradition itself lies rather deep down the tradition tree. By the time you unlock it, slave raiding will be but supplementary to your population management.
• Since the military power required to make successful threats also takes the navy into account, a viable strategy for Carthage is to continuously threaten Rome using the much cheaper fleet, despite in reality lacking an army to do real fighting. What's important is that issuing a threat forces a truce between the countries and thus, Rome can't attack Carthage. By itself it's meaningless, but in the meantime Carthage can conquer direct neighbours of Rome (bunch of push-over tribals), thus preventing any further Roman expansion, as Rome now borders a country they have a truce with. Rinse & repeat a few times and after a few decades of being bottled, Rome will be an easy pick, rather than the unstoppable juggernaut it turns into after unifying Italy.
  • This strategy eventually becomes Complexity Addiction, as a more straightforward way of crushing Rome is to have an alliance web with Rome's stronger neigbours, then declare war when Rome is fighting her first war. This becomes especially valuable after cultural integration became a thing, making it in Carthage's best interest to take over large chunks of Roman territory in one war.
• With a bit of patience and some Save Scumming, Sicily can be made absurdly productive. Numerous territories have the "farmland" terrain, decreasing the number of slaves needed for any surplus. Syracusian missions provide settlements with a modifier decreasing the number of slaves needed to produce one trade unit of grain. Carthaginian missions after conquering the eastern side of the island provide a modifier generating surplus resources by default, no slaves involved. All combined and properly spread, this can make the tiny island more productive than any other place on the map.
• Liburnian is the final answer to all your political issues, via Uriah Gambit. Need a way to get rid of someone? Give them a ship. Not a fleet, a single liburna. Here, an office of navy commander. Then, send them against a whole pirate fleet. Got captured? Not your problem. Died? Even better. The only downside is that it (obviously) requires a port. The best part is that due to being granted the office, you will increase loyalty of such characters, possibly placating them (and their family, too), while nobody is going to protest when they die in impossible-to-win sea battles. The only tricky part is to pull this fast, for each commander is paid a substantial 2.5% of your total income, which by mid-game can be a small fortune.
• Chokepoint Geography combined with building cities in the right settlements makes it virtually impossible to invade a country. If you have a border settlement that ends or opens a mountain valley, turn it into a city. Not for the profits of the city itself, but for the free 2 construction slots. Fill them with fortresses. This renders your border impossible to cross, as the invading army will be unable to pass through, while the level 3 fort can resist the siege for anywhere between 6 to 15 years - more than enough to muster and march the army to crush the invaders, even if you have zero troops at the start of the war.
  • This strategy doesn't work well if a province has multiple settlements where you need to build fortresses. In 2.0, each province has a number of points used to keep track of fortress maintenance; maintenance costs ramp up quickly once the number/quality of fortresses exceeds the number of points the province has. Every province has a default value of 5 points, which is enough for a level 3 fortress. However, two level 1 fortresses use up 6 points.
• In earlier builds of the game, playing as a small, compact power, just above a city-state, but not bigger than 24 settlements (and preferably below 10) to keep the status of Local Power, allowed the abuse of a handful of game mechanics, which, when combined, turned your country into a Pintsized Powerhouse, especially if all or at least most of your territories were within the capital region, simplifying the management. The sweeping changes introduced to the game with 2.0 rendered most of those advantages completely moot, but it was possible to punch waaay over one's own weight.
• Facing sufficiently large defensive leagues is normally a daunting task, even for a major power. However, they all have a Logical Weakness. Defensive leagues, especially those starting ones, are usually led by the strongest or biggest country in the league. To be able to be part of a league, one has to be either a City State or Local Power. In other words - having no more than 24 settlements. Sell your own provinces to the leader of the league for pocket change if they are very close to having 25 settlements. The moment that happens, they turn into a Regional Power, can no longer participate in the league and since they were the leader, their league itself gets disbanded. Synchronised properly, this allows the declaration of a bunch of wars on tiny countries and city states that are suddenly without any major alliance, leaving them exposed. And since they are at war, they can't form any new alliances of any kind, turning otherwise a tough challenge into a string of Curb-Stomp Battles, all in separate wars.
  • This was later nerfed by eliminating the disbanding part; while the new Regional Power is still forced out of the league, the defensive league remains in existence. Still, it is a good way to isolate the new Regional Power.
• The entirety of cultural integration mechanics introduced in patch 1.5 is for the most part counter-productive, doing more harm in the long term than it helps when simply used to add another culture to your accepted ones and keep them as such for the rest of the game... but it's a great tool for two specific situations, making extensive naturalisation of non-accepted cultures a breeze, rather than preserving them:
  • Seleucid Empire doesn't implode under the sheer weight of foreigners in it, as integration allows Going Native with Persians with grace, while simultaneously focusing on the plethora of the tiny minorities spread across the empire and turning them Greek(ish). Then you can keep ignoring Persians forever, or, once they become the only non-Macedonian group in the empire, remove their protected status and swallow them, too.
  • After conquering new territory with more than one culture in it, accept the one with biggest number of pops within your expanded borders, greatly decreasing local unrest. This also means the smaller one instantly becomes surrounded by "dominant" culture, removing penalty to naturalisation. For even better results, throw in military colonists. Once you are done with the smaller group, remove protected status from the bigger one, which now has to face both your own colonists and the former minority that already got naturalised. Romanisation never was this fast when going into lands with more than a single culture populating them, a reversal of the pre-1.5 situation. Ironically, since there are dozens of Greek cultures, it is possible to make them all completely extinct in Greece (or turn it into a homogeneous culture of the conquering Greek state) within 50 or so years thanks to "targeted" naturalisation and playing them against each other. Prior to the mechanics being introduced, you could have variety of Greeks easily existing all the way until late game, even if aiming for a Greek conquest right from the start.
• A nation-specific one: crushing Rome early as Carthage. A diplomatically-inclined Carthage can ally with multiple nations surrounding Rome, while fabricating a claim. After Rome declares war on a neighbour, declare war on Rome with the fabricated claim and call in allies. With the proper set-up, Rome can find herself at war with nearly every major power on the Italian peninsula. Even if prevailing in her own war, as long as Carthage can pry the Roman heartland with integrated pops from Rome, Rome is as good as broken. With a broken Rome, Carthage has no real rival between it and the rest of Western and Central Europe. To add to the brokeness, invading the Italian peninsula early and integrating an Italic culture with enough pops allows Carthage to access Italic traditions, traditions which include the construction of military roads and numerous improvements to heavy infantry.
  • In addition, Carthage can easily integrate a Hellenic culture to gain access to their unique inventions. So now, you have a Carthage that is a trading empire, has Roman military traditions and Hellenic technology. Early Game Hell notwithstanding, you can easily surpass the Roman capability of taking the entire Mediterranean Basin^note There is also a Violation of Common Sense aspect. To properly integrate Siceliote, Italic and Roman cultures and gain access to the related bonuses of Hellenics and Romans, Carthage must push in that direction from the get-go and start with Sicily. If you decide to first strengthen your base in Africa, this will significantly increase your total pop counter, meaning that even once Magna Graecia and Rome are conquered, their population will be too small in comparison to your total population, barring you from accessing cultural bonuses. However, despite sounding like a big gamble, taking over Sicily at the game start is one of the most straightforward moves for Carthage and you even start with a mission to do so.
• One of the Carthage's economic missions offer a choice of a permanent modifier to all ports in two regions (the biggest unit of land division). Two of them are insignificant buffs to cultural integration and fleet recruitment, but one is a solid economic bonus. Originally, ports were pre-defined to specific territories, so it wasn't a big deal and the bonus was barely noticeable, regardless of choice. However, since patch 2.0 turned ports into buildings (that can be built even in a rural territory), you can simply build ports in every single coastal province prior to that mission and the game will grant the bonus to all of them. Even if you then remove the port and build something useful instead, the modifier will stay.
• With changes introduced by patch 2.0, Scythia became absurdly effective, predominately because it's a huge tribal state with lots of land to quickly and easily colonize. Unlike typical scenarios, it just means more pops of Scythian culture following Heptadic religion (i.e. pops of primary culture following the state religion). On top of that, it's a Normal Fish in a Tiny Pond, since it's surrounded by tiny Greek states and push-over tribals. And if this wasn't enough, Scythians laugh at heavy infantry-based legions, the typical "killing force" of more advanced nations, for their main unit, accessible even as a levy, is Horse Archer (further bolstered by highly effective heavy and light cavalry), a bane of anything other than heavy cavalry, that's particularly effective at "default" compositions of levies and legions across majority of cultures. AI will never get to that critical mass needed for an absurd Scythian snowball, but even the most incompetent player can easily turn Scythia into a major power within just a few years. And once you "upgrade" your settled tribe into a civilized nation (for which the nearby Greek colonies are very useful), you're virtually invincible - even when facing Rome that spawns all over the Mediterranean, it is possible to just roll over it.
  • The only wrinkle is that the colonizable lands with Scythian pops lie outside the capital region. If the player is not careful, disloyal governors may cause a civil war.
• Legions are broken on three separate levels:
  • AI can't properly compose them, meaning it mixes too many units and just replicates its levies, wasting all the potential of the legions; AI is also notoriously unlikely to get the right inventions AND pass the related law to even have a "capital" legion at all, not to mention numerous legions.
  • They allow easy domination of the battlefield, due to picking just the most useful unit types and the above-mentioned issue with AI. Even when facing other human-controlled country, the one that simply starts with requirements to rise their own legion from a start will easily beat the other player that is forced to use levies and mercs instead, and if both sides have legions, the one with more cohorts inside will overrun the other in battle.
  • Sieges become laughable, since engineering cohorts work just like artillery in Europa Universalis series, offering massive, and more importantly, unlimited bonus to siege ability^note A siege ends when the counter hits 20, achieved by going through numerous siege phases, each adding +1, plus various other modifiers. This means having 19 cohorts of engineers - a feat perfectly doable by mid-game, or even having a purpose-made "siege legion" - will finish a siege in a single phase, because the counter will hit 20 no matter what. And of course various other things can affect it, decreasing the number of cohorts needed to achieve the 20 on the siege meter.

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