For example when you are playing as Czechia and you successfully take Slovakia, you will have an option to create Czechoslovakia so the cities and provincies in Slovakia will produce 100% resources like in the czech ,,homeland´´.
The same can be done when you are playing as Russia, when you take Belarus, Ukraine, Kazakhstan... you can form the Soviet Union
The same can be done when you are playing as Russia, when you take Belarus, Ukraine, Kazakhstan... you can form the Soviet Union