This isn't the most blantantly exploitive strategy available in EU2, but it is the most effective.
Once you get to be pretty good at EU2, your primary obstacle isn't the strength of your country, tech group, etc, but instead your BB score. Your goal is therefore to gain as many provinces for as few BB points as possible.
DOWing with a CB costs 1 BB point, and in an offensive war you pay 2 BB points per province. These are steep costs. Gor an example, DOW your neighbor and take three provinces and you will be waiting, depending on difficutly level, between 28 and 56 years to work off the BB points.
So you want to avoid making DOWs and taking land in offensive wars. This is where what I call alliance hopping comes in.
Generally, at least some of your neighbors will be at war with someone. Find who they DOW'd in the diplomacy window and join their opponents alliance. You are now in a defensive war with your neighbor. Take the provinces you want and you pay the BB min - 0 since you didn't DOW and 1 point per province you take. This works really well in obtaining vassals too.
After you are done with your current target, repeat to your heart's content. Leaving alliances only costs you 1 point of stab. You will occasionally need to bribe the leader of the alliance you want into, but a few hundred ducats for free BB points is a bargain.
Once you get to be pretty good at EU2, your primary obstacle isn't the strength of your country, tech group, etc, but instead your BB score. Your goal is therefore to gain as many provinces for as few BB points as possible.
DOWing with a CB costs 1 BB point, and in an offensive war you pay 2 BB points per province. These are steep costs. Gor an example, DOW your neighbor and take three provinces and you will be waiting, depending on difficutly level, between 28 and 56 years to work off the BB points.
So you want to avoid making DOWs and taking land in offensive wars. This is where what I call alliance hopping comes in.
Generally, at least some of your neighbors will be at war with someone. Find who they DOW'd in the diplomacy window and join their opponents alliance. You are now in a defensive war with your neighbor. Take the provinces you want and you pay the BB min - 0 since you didn't DOW and 1 point per province you take. This works really well in obtaining vassals too.
After you are done with your current target, repeat to your heart's content. Leaving alliances only costs you 1 point of stab. You will occasionally need to bribe the leader of the alliance you want into, but a few hundred ducats for free BB points is a bargain.