Nothing of importance would happen.
I'm serious, everyone is making these grand predictions about how the U.S will be totally destroyed if Trump becomes president. Am I the only one who thinks that a Trump presidency would lead to nothing? Neither Democrats or Republicans in Congress would work with him, and he'd likely be impeached within the first year unless he tones his policies down.
This is rash to say. Didn't Bush go to war pretty quickly? And he seemed much better until presidency (I believe). Maybe America will fill up the territorial ambitions of Greater Puerto Rico by annexing all the Middle East.
And you're wrong to think WWIII isn't possible. The mini-crisis that ensued between Turkey and Russia is evidence it can (and in my opinion) will happen given the right timing of events. If Turkey had invoked Article 5, its likely NATO would have to come to Turkey's defense. Things may seem peaceful in Scotland but the world is not by any stretch of the imagination peaceful. At the least extent expect many more proxy wars in the coming decade which would be equally disastrous.
Foreign wars and invasions are profitable. Complete destruction is not. There will not be a third world war, just probably more proxy wars.