The Great Sioux War was a massive genocide campaign done by the United States of America from 1865 to 1867. It was sparked mostly by the thirst for blood after the U.S' humiliating defeat in the War Between The States, as well as President Fremont's need to further Manifest Destiny, now that all of Canada belonged to the American nation. The War lasted for two years before the surrender of the Provisional Metis/Sioux leadership at Little Big Horn.
Prelude to War (1864-1865)
The prelude to war can be identified as the Treaty of Boston, which affirmed Confederate neutrality in American affairs. President Fremont, despite his fealty to the Democratic Party's anti-war maxims, firmly subscribed to the idea of Manifest Destiny, as he was from California. The Sioux's occupation of the Dakota Territory's land as their "reservation" triggered a hostile reaction from the Federal Government. When rumors of a Sioux-Metis Alliance rose in March 1865, Fremont could sit back no more.
War leading up to Red River Massacre (1865-1866)
The war's slow start and progress were an obvious sign of the United States' weakened war machine, however, as the campaign progressed, the U.S. Army grew more confident with each victory. Chasing Sitting Bull and Louis Riel from Dakota into Manitoba, they confronted each other at Red River. What started as a normal battle lead to radical amounts of death on both sides. Americans who were killed were frequently scalped and displayed as trophies, and Indians were frequently raped and buried in mass graves.
The Massacre (September 21, 1866)
On the dawn of September 21, 1866, General Grant lead his armies into battle, having received information on Riel's command post. Hoping to take him by surprise, General Order 398 was issued -- No mercy. Thousands of Indians were sent to their graves as US soldiers brutality grew with every passing hour. Riel was found and hunted down. He was brutally violated and hung from a tree by General Grant himself. This massacre has been a nasty stain on the United States' military history ever since.
On January 2, 1867, the Metis and Sioux accepted a ceasefire agreement by the United States Army. Meeting at Little Big Knee, the Metis and Sioux agreed to put down arms and cease rebellion. However, this rebellion wasn't exactly over. After signing it, all of them were rounded up, charged with high treason, and executed. The Sioux survivors fled into Russian Alaska or Confederate Oklahoma. The Metis' survivors marched hundreds of miles to Quebec, where they established New Metis.