Under the rules for taking forts introduced with Patch 1.10, you would need to have a army unit force 3 times greater than the current fort level so (Capital fort is 1 fort level and a castle is 2 fort levels making it a total of three fort levels) So you would have to have a unit of 9 to seige the fort. All you really need to do is raise your starting army to 9k by recruiting one more regiment.

I'm undecided if I really like the fort system introduced in 1.10 over the older EU3 system used until 1.9. There's a lot that goes wrong with it when they do updates and unit marching path generation is stupidly idiotic at times and often confusing as to why multiple units have to march unnecessary routes just to move over one province.

You can read more about the rules and mechanics of Sieges here:

http://www.eu4wiki.com/Land_warfare#Sieges

The reason why most states have level 3 forts in their capitals is because I haven't found many good places to put a castle besides the capital. In the case of New England the region is heavily crowded and three large neighbors (New York, Ontario and Quebec) are at the doorstep ready to pounce. The the New England states are, like the rest of the continent, to be guaranteed at least 1 level 2 fort somewhere and most were put in the capital if there wasn't a more suitable area to put them.

Thanks for responding, especially so quickly, but i feel like you missunderstood what i was trying to say.

I understand the mechanics of the forts and i was noting how difficult it is to play as one of those states in the northeast when each neighbor has a level 3 fort and no starting army big enough to expand.

That being said, you are right about the cluster of small states in the North East and how they each need a level 2 fort and that it should be in the capitol. While this protects the smaller new england states, i also feel like this limits their ability to expand.

Obviously you're the developer and you know way more about it than i do.