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).
Double taxation treaties are very common. What I’ve been told by US coworkers makes the US stand out is that you still need to file your taxes with the IRS, even when living abroad. No idea if that’s actually the case.
I have lived outside my native country for a while and only had to file taxes in my country of residence (neither of which is the US), because there’s a DTAA in place between the two.