The American Union was formed after the American Revolution involving all 19 American colonies against the then British Empire, with the Revolution a succsess the American Union was formed by the founding President George Washington adopting a flag of 19 stars representing the states of the Union.
North Mexico borders the Union to the south with Canada and the former state of Alaska (now the Free Nation of Alaska) to the north.
World War 1
The American Union, fresh out of the Great Depression, with a moderately large army, navy and air force, set up border patrols on the Northern Mexcian border after booze traffickers attempted to smuggle alchohol across the border. With the Russian elections happening in the winter, one of the world's superpowers was on a knife edge with the Weimar dictatorship was performing unauthorized military exercises near the Russian border.