When did Custer's new theory start?

Custer's new theory, which focused on the importance of military intelligence and understanding Native American tactics, began to take shape in the late 1860s, particularly during the Indian Wars. His experiences and observations during campaigns against various tribes, including the Sioux and Cheyenne, influenced his strategic thinking. However, it wasn't fully realized or implemented until his final and fateful campaign in 1876, leading to the Battle of the Little Bighorn.