Not much happened honestly. It was a military exercise in 2015 and reactionaries were convinced by Alex Jones that it was a training exercise on how to confiscate guns and put all conservatives in FEMA camps. The military used American cities for the training, like in abandoned buildings and Walmart parking lots and stuff like that. Nothing at all happened but the chuds were very riled up about it to the point the Texas government sent state militia and cops to surround the military facilities just in case I guess.

It's also far more likely that the exercise was about fighting a potential Chinese invasion.