Taking advantage of the fact that Nevada's capital is so close to California, California utilizes their colossal populations and raises a militia to storm Nevada. Extreme temperatures slow them down, but Carson City is quickly besieged and taken. Oklahoma is unable to put up an organized resistance against Texas, quickly losing most of its land and becoming a puppet state. Meanwhile, forces in Mexico quickly militarize, scaring the likes of New Mexico and Arizona. A fragmented US is an opportunity they will not pass up.
Did the Northwest Territory just, stop fighting? I'm not really sure, but I'll say they sign a treaty.
