Hm... And maybe one or two (or more) of them opt not to join said federation.some way to kill the unification attempts of Italy and Germany would create tons of small independent citystates and small duchies spread all over.
They might still create a federation not unalike the 'ideal' EU, but they would still be a ton of small city states none of them strong alone.
At least in case of Italy a good way to butterfly it, would be to stab Napoleon before he looks that way