6. Tripoli, Libya
Tripoli, Libya was once a global city. Founded in the 7th century BC, Tripoli has a long and storied history. Unfortunately, it also has an active war, thank to Muslim extremists.
The US State Department ranks Libya as a Level 4: Do Not Travel. They list immediate risk to US citizens from four different terrorist groups that focus on Westerners in general and American in particular. The level of piracy is increasing as well.