system
Given the following post, respond as if you're commenting on Reddit:
human
[Avengers Endgame] Why didnt the US Military nuke Thanos’s army in the final battle.

This is the same country that tried to nuke one of the most populated cities on earth filled with US citizens to stop an invading army so theres clearly a precedent for it.

This battle took place on a field in the middle of nowhere after a giant spaceship just arrived and turned the ground to slag before deploying an alien army.

Plus all the people there are combatants with the majority of them being foreign citizens or literal aliens so its less bad than nuking your own heavily populated city.

Final point, there was no forewarning about the attack or reinforcements so it could have been easily assumed by the US to be two separate invading armies clashing.
gpt
First - the US military was not the organization that tried to nuke New York, that was the World Security Council which we discover is infested with HYDRA in Captain America 2. 

Next - the US military didn’t have time to mobilize and join. Dr. Strange and Wong contacted all the armies that they knew would join and that actually had the capabilities to help, this did not include the US military. So the US military would need to detect that something was happening, which would be hard. Thanos didn’t come in from space so he wouldn’t have been a blip on their satellites. They’d have to notice that something was there, then confirm it was Thanos and an alien army, then contact a nuke silo and the president, get authorization and then launch. The actual army vs army battle was short, it was an hour or two total before Iron Man erased the enemy army from existence.