America is not enforcing its laws on some random people outside its borders, its regulating the behavior of people who are very much subject to our legal system. I am quite surprised to see there's a contingent of folks who think that leaving our borders means you can do whatever you want and expect to be welcomed back
The Alien Tort Statute applies specifically to "aliens" not Americans. It's about holding foreigners liable for conduct on foreign soil in U.S. courts.