The Europeans have no stomach for fighting, and in any case, any US civil war would probably mean they would have their hands full with Russia.
And the US would still control its nuclear weapons. Even if a rogue leftist US government invited them in, it would be a hard offer to accept, if for no other reason than such invitation would be a good way to cause US strategic forces to remove themselves from the US command structure.
My guess is everyone else would sit it out and wait for the dust to settle.
Because, that's where the power still lies for now. Guess what? 2016 happened - the ballot box. Now it's time for 2018. Consider just these 4 points alone: Korea reconciliation, economy/taxes, ICE/immigration/wall, FISA/coup.
All four topics will dominate the political discussions leading up to November. Trump needs just one more (mid-term) victory under his belt to really begin acting. Any bets on where the US strategic focus then turns?
Would it be the Spratleys? How about Syria/MENA? May I suggest the greatest strategic threat posed to the USA is California in a state of insurrection? Now, from a born/bred native, I can assure everyone that a significant number of residents feel like they are under some form of occupation. The state will get no support for us - we would welcome a federal occupation.
Take out California, and the entire proglib plan for conquest evaporates. It's the lynch pin, and thereby the obvious target for Trump to attack when he is good & ready.