Not typically for international flights, and even for some US domestic carriers. Same goes for most of the rest of the world (e.g. Asia) which is what I was actually thinking about. Brazil has free luggage mandated in law.
Even when you do have to pay in the US it is typically very generous. Larger size and weight allowance, and you won’t get dinged for being even a few kilos over. And the bottom tier of frequent flyer programs (which is usually trivial to get and keep) waives all these fees anyway. I can’t remember the last time I paid for luggage allowance outside of a trip to or through Europe.
Even when you do have to pay in the US it is typically very generous. Larger size and weight allowance, and you won’t get dinged for being even a few kilos over. And the bottom tier of frequent flyer programs (which is usually trivial to get and keep) waives all these fees anyway. I can’t remember the last time I paid for luggage allowance outside of a trip to or through Europe.