Final answer:
Colonel George Custer lost the Battle of the Little Bighorn due to underestimating the size and strength of the Lakota Sioux warriors who surrounded and outnumbered his detachment.
Step-by-step explanation:
Colonel George Custer lost the Battle of the Little Bighorn due to several factors. One key reason was his underestimation of the size and strength of the encampment of Lakota Sioux warriors led by Sitting Bull. Custer and his men, who were the aggressors in the battle, were outnumbered and surrounded, resulting in the annihilation of Custer's detachment. Additionally, faulty reconnaissance led Custer's column to charge into battle without the support of the other two columns of cavalry.