Custer wanted to fight 1’500 warriors.
He fought 1’500 warriors.
Custer wanted to surprise the enemy.
He surprised the enemy.
Custer thought that the Indian organization was poor.
Indian testimonies talk about friendly fire and mess on the Indian side.
No underestimation here. see http://www.custerwest.org (English version)
Okay, then he obviously overestimated his own prowess.
Something didn’t work out too well.
The classic underestimation of the enemy came years earlier about 100 miles south of Little Big Horn. Lt. Col. William Fetterman, upset with the Indians' hit and run tactics, said, "Give me 80 good men and I'll ride through the whole Sioux nation." Ironically, a few months later, Fetterman and 80 men were decoyed by some Dakota warriors (led by Crazy Horse) into an ambush. There were no survivors among the soldiers. This was the probably the defining battle in Red Cloud's War, the only war that the Indians won (at least temporarily).
The massacre site is just off I-90, north of Sheridan, Wyoming. The massacre site and nearby Fort Phil Kearney are now a historical site. If you are passing through, it's worth a stop.