Requires all visitors to be sponsored by a legal resident or citizen.
Iran doesn’t even have an American Embassy anymore, thanks to the tense Iran hostage situation that occurred there in 1979.
North Korea requires all visitors to book a full package tour before visiting. During your visit, you’ll be required to stay with your guides the entire time. The lack of North Korean embassy in the U.S. means you’ll need to travel to China before booking a tour.
Syria is in the midst of conflict, but if that doesn’t deter you, the nearly impossible-to-get visa might. Since each visa has to be approved through a complex process, potential visitors face an indefinite wait to be approved or declined.
The relationship between Cuba and the United States is relaxing slightly, but the current travel regulations still don’t allow anyone looking for a a good Cuban sandwich and a Caribbean beach to book a flight. Unless you can prove that you’re in Cuba for one of the official reasons, you’ll have to wait longer to visit.
Somalia is known for the vast number of pirates roaming the seas around it, which should be a good reason not to go.
If Angola on your must-visit list, you’ll need to be okay with some serious expenditure before you even find out if you can go. Before you can apply for a visa, you’ll need to pay the application fee and invitation fee, then book plane tickets and hotel stays.
As of 2014, the Central African Republic has no American Embassy, and all U.S. visitors must apply through the French Embassy. Add in the fact that the borders of the CAR are extremely restricted and you’ve got one place that doesn’t want to see any American citizens.
Lybia and the U.S. have been at odds for most of the 21st century, and, the U.S. Embassy closed there in 2014.
Algeria is another country that wants visitors to showcase their ability to pay for their trip before they arrive. First, book your hotel, then receive a certification of accommodation. Once you have that, you’ll have to communicate with a local travel agency to secure an invitation.