why: so the government won’t be able to use your money for whatever the fuck they’re planning for the next 4 years.
as a traveler, none of my money has been funding Israel, for example.
one-step method: you basically fill out one extra tax form called FEIE while you’re doing your taxes, write down the dates you were outside of the country, and then since you aren’t in the country and are not receiving any services from the US, you don’t have to pay income tax up to a certain amount (it’s a little over 125k this year).
https://www.fatf-gafi.org/en/countries/global-network.html
I am sure there are better sources than this, but I am going by what I was told by the bank when I opened an account here in Japan. And maybe it does not only apply to Americans, but I was told at the bank that I had to fill out additional anti-terror related paperwork with US details specifically because of US citizenship.