Yes, US citizens need a visa to travel to London.
Yes, a US citizen does not need a visa to travel to London for stays up to 6 months.
Yes, US citizens need a visa to travel to Ireland.
Yes, US citizens need a visa to travel to Kazakhstan.
Yes, US citizens need a visa to travel to Russia.
Yes, US citizens need a visa to travel to Uzbekistan.
Yes, US citizens need a visa to travel to the Philippines.
Yes, US citizens need a visa to travel to Saudi Arabia.
Passport and airline ticket that's it. Before you land British authorities will have you fill out a form asking you how long you will be in the country, where you are going, and why you are there. It is pretty simple to do.
Yes, a US citizen needs a visa to travel to Russia.
May be Afghanistan is the only friend country for USA, in which US citizens need Visa to travel.
Yes, US citizens need a visa to travel to Uzbekistan.
Yes, most foreign nationals need a visa to travel to the United States.