When they get on your nerves or have something you want, preferably both - Edit 1
Before modification by Isaac at 16/08/2010 05:04:52 PM
Once one or both of those conditions are met, especially if lots of other places feel the same way, then you only have to check two other things 1) Can we take them? and 2) Find a Cassus Belli. 2's very easy.