Id first look at the US travel warnings for countries, and automatically rule those countries out. The warnings are there for a reason. As for traveling to Africa, definitely check into what ever tour operation your looking at, a lot of countries there are definitely not safe. (I was in Egypt 20 years ago, and even then it definitely was not a safe place to be).
Id check for credentials (I always solo it, so not sure what credentials to look for), Id want to talk to people that had previously taken the tour. (Theres so many bogus operations out there, its unbelievable (taxi driver in Cairo tried to tell me he ran the Hyatt's tour organization, the jewelry store in the hotel, and drove a taxi as well. ( He even went into jewelry store in hotel and stood behind counter to try and prove it lol))). For places like Africa, Middle East, South/Central America, your much better off dealing with a US bound travel group compared to a local, worst comes to worst, you have ability to seek reperations. Good luck getting your money back from most local ones, just aint going to happen.
Id go to Europe, and do it solo. So much to see, so little to worry about.