Migrating with the barbarians in Imperator: Rome is probably the only way to play them. You can, of course, play in the normal fashion and simply conquer states around, and slowly take over the unclaimed real estate. But this won’t lead to any sort of real power, as all those provinces are devoid of significant population and cities.
Such a setup doesn’t allow for much income, and without income you won’t be raising armies, and without armies you won’t be conquering anyone.
Migration. Any settlement with at least three pops can start a migration, with up to 20 pops mobilised at once. The only cost for pressing the button is a decrease in your stability. The settlement needs to have your integrated culture as it’s majority culture.
These migrating pops turn into light infantry which cost no upkeep at all, save the food that they will consume.
Settling and re-migrating
What makes this method particularly powerful is settling. Obviously, you want to stop moving at some point and find a new home for your horde, but we’re not quite there yet.
To settle into a settlement you need at least as many migrating cohorts as there are currently pops of other than your primary culture. This will then make the settlement yours. To re-migrate from there, you need half of the pops to be of your culture. Settling costs nothing, save for the cohorts being disbanded.
Once the dominant culture of the territory is your chosen one, you can then migrate again. The important bit is that all pops that migrate will turn into your primary culture. This is the most important part, as it allows you quickly to double your migrating bands in size, assimilating and absorbing all in its way.
Stability, religion and laws
The base cost of the migration action is eight stability. Decentralization affects this, decreasing the cost by up to 50%. It also means that your stability will be running very low as long as you are migrating, as it should as very low stability also means higher stability gain.
Another way to up the stability is to use political influence for divine sacrifices. The faster you get your stability up, the faster you can migrate again.
Before you migrate and use up your stability you might want to take a look at the laws. There are four of these, and they all require at least 15 stability. Passing them will cause decentralization to increase by 0.40% per month.
You can realistically gain up to 0.50% stability per month, and at lowest it costs 4 stability to migrate. This translates to 3 provinces per year. You can optimise this further by conducting more sacrifices, paying attention to your leader, picking the right omens and choosing the right option in events.
Remember to settle with one pop
Once you understand the basics it’s time to seek out your fortunes. It’s best to seek out provinces that are populated, as the main idea is to simply grow your band of barbarians.
One useful tip here is that after you migrate, always settle the province with one pop. This way you’ll gain access to food production, and make sure attrition won’t whittle away your migrating hordes.
It’s also useful in the sense that the population will keep growing, and sooner or later you can migrate again.
Depending on which tribe you start with, you might have access to a lot of empty settlements. These can be claimed, with three or four pops usually joining your band afterwards. And if you have the money to move the pops around, you can instantly mobilize the entire province for one stability hit.
In fact, this is a must in order to grow the barbarian warbands. Once you have a couple of these roving 20k stacks, you are ready for your first war.
Wars are useful, and necessary, as the most populous provinces are already claimed. Remember that your units cost no upkeep, so it’s pretty easy to overwhelm your smaller neighbours this way.
The downside of this warfighting is that you need at least 30 stability to declare a war. This means that you need that this cycle of fighting and migrating takes a lot of time.
Moving your pops around
To make sure you get the most out of your stability investments you should always move pops from other territories to the one you are about to migrate from. There are some limitations to this, such as being in the same territory or adjacent, so you might need to scratch your head a few times when making the calculations.
This is also why you need to resettle the territories. That one pop will quickly turn into two, and you can then easily move all of them into one province and migrate with an army of 20 000 light infantry.
This does obviously cost money too, but since you shouldn’t be paying any upkeep (disband all standing armies) there should be no economical concerns here.
Don’t forget about diplomacy
Though you’ll quickly amass vast armies, you shouldn’t forget about making allies and claiming territories either.
First of all, your armies are weak. You might have a ton of light infantry, but with equal numbers, they are always routed. And given that your enemies are going to usually be at least two or three nations at a time, you will find yourself in some equal battles.
And the more losses you take, the faster your war exhaustion is going to build up. Not to mention that conquests without claims are going to cause a lot of aggressive expansion, which is not gonna help with your stability gains.
To even this out you need strategy and diplomacy.
Concentrating the population on one, two or three provinces to migrate them is going to save you some stability, which means you don’t need to use all your political influence on divine sacrifices. This, in turn, allows you to fabricate claims on your neighbours. Without claims, it’s pointless to go to war.
You can also gain claims from missions, which for the barbarians are very generic, but do exist. Or more importantly, by consulting your war council.
Make sure to check who your enemy is allied with, and lay claims on them too. You can gain vast areas, and huge populations, by taking over entire tribes at a time. One useful tip is to simply settle into an empty spot next to your enemies borders, which allows you to lay claims immediately.
It’s a numbers game
Let’s get on with the warfare then.
Your strategy for warfare is quite simple: keep your troops together and beat up anyone foolish enough to venture close-by. Your enemy might beat you in a one-on-one fight, which is why you should always aim to make it a ten-to-one fight, or as close as possible.
As a migrating horde, you also have access to clan retinues. These will start small, but they will nonetheless add some thousands of men to your retinue. More importantly, they add units that are more powerful and hence more useful
Your basic strategy is to simply siege down the forts and claim victory. Do it right and you won’t really even need to right battles. But if at all possible, beat down the enemy armies so they won’t march around claiming your unfortified homelands.
Your migration cohorts reinforce from your manpower, and you won’t have a lot of this at the start. The same applies to the enemy, but you should still be wary of overplaying your hand and losing all those pops to attrition.
Onwards to Rome
All of the above of course builds up to whatever your eventual goal is. To recap, your initial goal is as follow:
Take over smaller states surrounding you, preferably other barbarians.
Lay claims, conquer, settle, repopulate and migrate entire regions at once.
Build up your migrating armies, but don’t entirely empty the lands of people.
Move on to bigger and bigger enemies.
Keep your decentralisation high and build up stability constantly.
Once you get to the real enemies it’s a different game. It’s usually wiser and easier to overpower all of the barbarians than it is to move early against the establishes states with their standing armies, cities and fortifications. Especially as they might play the attrition game against you.
This is why you won’t be actually migrating at the start, as much as you are simply building up your powerbase. I would suggest taking over Germania and the Gauls, and after that simply mobilize everything and slowly move on towards the city-states. Whether you want to conquer and settle, or just de-populate the known world is up to you.
Remember that one of the points of migration is to convert the pops to your culture. The bigger nations start with hundreds if not thousands of pops, and you need equal numbers to make sure you can convert them too, or at least not suffer too many penalties and rebellions when you eventually settle down.
Finally, you don’t want to wait too long until going after your prize. The reason for this is simple: technology. When you migrate you’re not going to be researching tech at all, which means that eventually, you fall too far behind to make any sort of a stand on the battlefield, no matter what the numbers look like.
However, you can gain tech by pillaging and razing locations. This can also yield money and political influence. Be careful not to burn everything to the ground.
One final tip: you can settle your migrating hordes during war, which will flip the province to your control. Be careful though, as this will decrease the size of your army, and as it is not possible to migrate during war.