DoW seems like the best defense.

[Iry]

I've been playing a lot of BNW games and have won about a dozen on Emperor or higher now. The game is actually pretty good at building up units and then smashing them at you simultaneously. On the other hand, the game seems terrible at mounting any kind of coordinated offense after this initial rush.

So if I start a game up and it looks like I'm near one of the classic warmongers? I just declare war on them preemptively. It works like a charm every single time, and they never build up enough units to really threaten me. Just make sure you can get your trade routes safely to some other civilization.

 

[Byzantine Bomb]

I'd have to agree with you, after their initial assault, the AI does a poor job of re consolidating and mounting anymore large offenses. After the initial invasion, its survivors (Or replacements) go on solo missions to burn women and steal your crops. If you beat back a surprise invasion, follow up with an offensive of your own and you probably won't encounter much resistance, in my experience anyway.

 

[Jaymax]

I think one of the biggest flaws is the fact that the AI makes no attempt to hide it's going to invade you. When you see them lining up units directly behind your border, and then bringing in a great general, you immediately start building up your military, kind of negating the surprise part. The human player, if they survive the invasion, (most of the time anyway) then proceeds to invade the AI lands since it just lost most of it's army in a ridiculous invasion.

 

[HorseshoeHermit]

The fact is, under the hood, the A.I.s are all fascists. They believe their rights to the land comes from power, and they demonstrate their power over the land by massing their (cheaply waged) soldiers.

They aren't simply posturing, nor are they "telling" you they're going to invade. They're jockeying for position to defend what's theirs. At the point where your position is tactically weak to the position they can produce, they'll contemplate war (if they don't like you, and/or/meaning they really want your stuff).

I expect the reason they don't do well afterwards is - well, first things first: The A.I.'s (war) strategy is terrible, and its gameplay is governed by thematics, not actual sense. Since its strategy is terrible it doesn't matter how good it lines up the soldiers, they're going to die an awful death. And behind all that, the A.I. each makes decisions just based on a flavour that disposes it to take certain kinds of actions by chance whenever it has a choice.

You'll find that if you maintain an army, and use the terrain sufficiently, the A.I. will simply put up with a strained relationship with you for all of 2050 years. But this is only when they don't have their ridiculous economic boosts. The higher difficulties give the A.I. the ability to (think) it has more than you, causing its (fascist, as I said) ideology to invoke war.