As the Mexican attack on the United States in January 2050 came as a big surprise, they managed to inflict much damage on US-territory. Mexico was passively backed up by the Southern American coalition (SAC), hoping to finally break the everlasting influence of the US on Southern American politics. They also agreed on dividing up the territory of Guatemala, Honduras, Nicaragua, Costa Rica and Panama between Mexico and The Southern American Coalition. The attack of the latter on Panama in July 2050 brought Argentina, Brazil, Colombia and Chile into the war against The SAC, while Bolivia and Ecuador joined the cause of the SAC in January 2051.
While US-troops in the western states where able to hold off most of the Mexican attacks, eastern states even became briefly occupied by Mexican troops in June and July 2050. Although dearly needed, the western States refused to send their National Guard battalions into the east, fearing to need them to withstand the Mexican attacks. When troops from US-bases the Pacific Ocean and a relief force from Australia arrived in San Francisco together with the carrier group of the USS Enterprise, Mexican troops were forced to withdraw back to the border. Still, US-troops were unable to bring the war onto Mexican territory until July 2053, when they dropped a neutron bomb over Mexico City, killing the augment dictator and over 21 million people. This caused the remaining government to capitulate immediately.
After the cease fire was negotiated, western and eastern states would continue to struggle over resources for the rebuild. Given the denied help in 2050, the USA would finally split into the Federal States of Northern America on the east coast and the United States of Western America, while Alaska formed a union with Canada.