So far, having individual small countries seems to keep the centralisation at bay for longer than just having states in a federation.

(Look at Germany, Austria, Australia, the USA for examples of the latter. Interestingly, the UK is legally not made of federal states, but in practice they have granted more autonomy to eg Scotland over the years. And everyone knows that Scotland would secede and get away with it, if there was a power grab by London. In that sense, they are more federal than the US, where secession is very much verboten.)