A lot of bad things can happen.
I have been deployed with the military on small detachments and had things go to shit. The difference is you have the might you hope of the US Military.
We were in SE Asia for a POW/MIA dig in Vietnam during a hurricane and tidal wave, we were able to get out of there and get out of there all of us together. But it was sketchy.
Here in Europe I was at a Christmas market that got bombed as we were driving home from it. What a difference an hour made.
I was at the US Embassy in Canberra when a guy with a truck full of his own urine and improvised explosives stormed the gate. I was on the back gate walking to my car when it happened. Got lucky, they were locked down for an entire day trying to figure it out.
Watched with a very suspenseful eye from a ops center when Bengazi went to shit. Abysmal leadership with Comrade Clinton when she fucked those guys over.
The list of places I am done with is growing.
Probably easier to list countries and regions I am still going to travel to.
Africa: Botswana, Namibia, Zambia, and South Africa is still on my list. Uganda and Tanzania is not because of cost, more than anything else.
South America; Argentina
Europe, pretty much all of Northern Europe is ok. Though, there are a lot of cities in Europe I am done with. Even here in Germany.
Australia, Japan, New Zealand, South Korea, Singapore, I am on the fence about Krygizistan and Mongolia.
Canada, Greenland, Iceland, that is probably the end of it.
I have been to 41 countries and lived in 5 outside the USA for years, and spent months in another 6. I am over 50 and I have spent 16 years of my life outside the USA. Considering I will probably only travel for the next 15-18 years, I think the list of what I have left is good enough.
I consider myself to be a fairly seasoned world traveler. You need to figure out some plans to get out, sometimes you have to accept that as the risk. You may not get out.
Here in Europe the problem is going to be "random" acts of terrorism. Christmas markets, stadiums, concerts, that type of thing. Though flooding and mass wasting events (landslides) are common in most of Europe and that might be your undoing.