A vacation on "the roof of the world" will enable you to experience a wonderful Tibet tour closest to heaven.
The boundless plateau, snow peaks, the holy lakes, and pure Tibetan Buddhism culture are all so overwhelming that you don't even want to blink just in case you miss anything.
Thanks to modern traffic, it’s very easy to travel in Tibet from the US.
There is no direct flight from the US to Lhasa, you need to fly to a China city like Beijing, Chengdu, Shanghai ect, then transfer to Lhasa.
As a foreign traveler, American must have a China Visa and a Tibet Travel Permit to enter Tibet.
You need to get a Chinese visa in your home country.