Income is also taxed if it's generated outside America as long as you're an American citizen. Some people who emigrated to Europe as a child got quite a nasty tax bill for decades of untaxed income when the USA found out that they're still American citizens, for example.
Many countries have tax law to deal with this type of American bullshit but it's still something to be aware of.
Many countries have tax law to deal with this type of American bullshit but it's still something to be aware of.