This guide is to serve the purpose of a remedy to strategic failures on the non-battle level. Many a time have I watched myself and others fail campaigns for not covering all your bases. Both literally and figuratively. Let's get started.

Going to war in this game may be a routine thing, but if you want to be careful, there are a few things you should probably know so you don't get knocked off your high horse.

-Be wary of your own imperium and relative levels of army strength between you and your enemy. As your empire grows, so will the amount of factions that will band together to stop your reckless expansion, you terrorist. For example: When playing as the German Confederation, make sure Rome and Avernii haven't become great friends. You may end up stuck with the now dying faction of Carthage, and the Dynamic duo, as it were, would control half the map.

-Certain factions are suicide to try and fight. The greeks and some barbarians are absolute asshats when it comes to attacking them. If that expansion is key, try to get some allies to flank them. On the other hand, some factions can steamroll half the continent in 15 turns. Damn Parthians. The rock paper scissors style goes like this: Greeks can beat back the Eastern factions, Easterns have the cav to fight the barbarians, and Barbarians can break the Greek lines. The Roman and Roman-esque factions like Egypt (and Rome you ♥♥♥♥♥♥♥) are special cases, their rosters are balanced. Only fight if you have the manpower.

-The bonus gotten from territorial control is larger than many give it credit for. If nothing else, go to war so you can take the province and start to create a war machine. Example: The provinces around the Black Sea (Crimea and the like) are key to hold because the ocean access and therefore trading opportunities are huge. It's also easy to defend.

-Factions with dangerous late game may be worth killing up front. Parthia is particularly dangerous as the cav spams are real with these ♥♥♥♥♥♥♥♥♥♥♥♥♥. Iberian factions in Spain are also dangerous if left unchecked. While the simulation may have idea varying from these here, keep the people who cause the most trouble from being trouble in the first place.

You must plan your war even before you declare one. First, make sure your treasury is stable. War in debt is no war at all. Troop recruitments and Merc recruitments rely on it. Money is just one side of the issue. Public order should be taken care of first, because it could get out of hand and a rebellion is not easily combatted when your a whole province away. Diplomacy can be an issue too, try to keep your non-target factions at least complacent so your not fighting 3 wars at a time. Finally, units themselves. Tailor your armies to be able to fight your enemies. This stage is important at almost all times. Spies can be a good way to see what forces your enemies are stocking up on, as well as checking the garrison of a settlement (to check a garrison, click on the town and look at the overview. If you have the information on the town, usually from spies, there will be a small fortress icon that you can mouse over to see garrison).

For reference:
-Eastern: Has good Cav, bring spears, beware their archers.
-Hellenistic: Pikemen and spears to boot, Swords and missiles are best.
-Barbarians: Mostly spears, but a few OP sword units (Oathsworn). Swords and Cav recomended.
-Roman: Best swords in game, but good all around, so counter with such. Javelins>Archers.

These are only general rules, as some factions are exceptions. Only way to truly know is spies.

Easiest bit. When you declare war, ensure no foreign powers may get on the wrong side. If you have allies, make sure that they like you more then they like them, else betrayals may be abound. If you have no military allies, immediatly after declaring war, ask friendly factions to join your war. You may have to barter a bit, and be wary; the more wars a faction has, the less it is able to help in yours.

Yes, that title is a joke. Any how, Now is when it gets real. This part of the guide can help you, even if you are not the aggressor. This game has many routes around the area, be careful not to forget one of them. The enemy will surely take any way they can to your settlements. War strategies change from culture to culture, so here is a quick rundown.

If you are _______:
-Barbarian: Ambushes and raids are the way to go. Mountain landscape makes tons of small chokepoints around the map, ensure you control these. Due to the abundance of spear units, the more elite, the better.
-Eastern: Map is more open, so I find rushing as fast as possible is most effective. Use Cav without modesty, as the enemy usually doesn't have the mindset to do so.
-Hellenistic: Your pikes make for good defenders. Fortify positions as much as possible, let the enemy come to you. If they wont take your bait, move a secondary force to attack their position, keeping in mind you want to stay as close as possible so you can reinforce the secondary army.
-Roman: You can do almost anything, the Romans are versatile and powerful, and their central location gives them the ability to adopt any style based on their location. It's why the game is titled Total War: Rome II.

Lastly, spies. Use them to soften up an army before hitting it. If you tag team 2 agents you can not only perform 2 actions, but hit 2 different targets, like a town and an army. It is unwise to waste agents, even if you know they will fail, it could be good experience for them.

Now, the goals for your war may vary a bit, but this is a general situation list to go over to end a war:

1) You want out, bad: For whatever reason, whether you are getting your ass handed to you, or you are at a stalemate, or anything, you need out of war. If so, just ask them for a peace treaty. Now, they will probably say no, because you aren't kicking their teeth in, so fidget around with the other diplomacy options, they have to accept one day.

2) They are asking you for a treaty: At this point, if your goal is accomplished, it may be wise to get out of war. Depending on the urgency they ask you with, you can extort the living hell out of them, maybe even confederate or make satripy. Go ♥♥♥♥♥♥♥ wild.

3) You want to absolutely destroy everything to do with the faction: Ok, you sadistic ♥♥♥♥♥♥♥♥♥♥♥♥, you want to make everyone in the faction starve and cry while you laugh like a ♥♥♥♥♥♥♥♥ hyena (or as I call it, "playing the game correctly"), then just ensure that the faction has no settlements and no armies left. Factions without a settlement get heavy attrition, so mopping the floor with the remaining forces is easy.

Final Note: War is hell. Unless you are an omnipotent, flying spirit that controls all of the generals of one faction into acts deemed inhuman. THEN war is fun.

Final Final Note: ♥♥♥♥ the Arverni.