Progressive movements are to be supported, reactionary movements are to be opposed. If a regional group wishes to, say, reinstate capitalism or feudalism, then this is to be corrected as bloodlessly as is feasible. Impulses towards reaction fade over time as socialism solidifies, but they definitely exist for at least a few generations after socialism is established.
National liberation is a pre-requisite for socialism, only then do borders begin to fade. In the interim, an internationalist federation of socialist polities would exist.