BUFORD, N.D. — At around 3 p.m. Thursday, a group of riders on horseback and in vehicles arrived at Fort Buford. The group was jubilant, chanting and cheering as the sound of a hand drum echoed across the historic site. These riders — members of the Modern Day Warrior Movement, a grassroots-led organization based in Poplar on the Fort Peck Reservation — had been traveling for four days, beginning from Poplar on June 7. Each day, they traveled be…