These are the specific warnings issued by the US State Department. Basically, as you get further down the list, the situation gets worse. You can also click here for further details:
Security warning for some regions:
Colombia and Mexico.
Security warning for entire country:
Algeria, Saudi Arabia, Russia, Honduras, Djibouti, Venezuela, Iran, El Salvador, Burundi, Niger, Mozambique, and Haiti.
Defer non-essential travel to some regions:
Philippines, Kenya, Mali, Mauritania, Israel, West Bank, and Gaza.
Defer non-essential travel:
Guinea, Liberia, Sierra Leone, and Pakistan.
Avoid all travel to some regions:
Ukraine, Nigeria, Cameroon, Democratic Republic of the Congo, Sudan and Chad.
Avoid all travel to this country:
Afghanistan, Lebanon, Iraq, South Sudan, Somalia, Lesotho, and North Korea.
Citizens remaining here depart immediately:
Central African Republic, Libya, Syria, Eritrea, and Yemen.
Sophie-Claire Hoeller is Thrillist's über-efficient German associate travel editor, and has had frequent flyer status since she was born in a Lufthansa terminal. Follow her @Sohostyle.