The time the United States of America splits into the Republic of America and the Colonies of America is said in Champion when June Iparis goes into the simulation room during her visit to Antarctica.
"The United States of America-also known as the USA, the United States, the US, America, and the States-was a prominent country in North America composed of fifty states held together as a federal constitutional republic. It first declared independence from England on July 4, 1776, and became recognized on September 3, 1783. The United States unofficially split into two countries on October 1, 2054 and officially became the western Republic of America and the eastern Colonies of America on March 14, 2055."
-Champion by Marie Lu