The "isolation" of the USA was more formal than substantial (in terms of trade they were well connected to the rest of the world, and ideas circulated widely even before internet).Despite the revolutionary events in Europe, US history, in my opinion, won't change much: America was in isolation during this period and focused on the continent. The divide between north and south would remain even if immigration from Europe is diminished. I'm not an expert on US history but I think that a civil war was unavoidable as long as the comtrasts between north and south remain. Abolitionist would still rise and European events would not influence the New World as much.
There are very few things, if any, which are truly unavoidable, in particular if there are significant changes almost next door (and Europe was almost next door).
12 years from the POD are quite a significant stretch of time to generate changes, even if the POD happened a few thousand kilometers away.