Their (Mormon) hostility to the lawful government of the country has at length become so violent that no officer bearing a commission from the Chief Magistrate of the Union can enter the territory or remain there with safety. . . . I accordingly ordered a detachment of the army to march for the City of Salt Lake — as a posse for the enforcement of the laws. — President James Buchanan's proclamation, Deseret News, June 16, 1858

We are invaded by a hostile force who are evidently assailing us to accomplish our overthrow and destruction. . . . Our opponents have availed themselves of prejudice existing against us because of our religious faith, to send out a formidable host to accomplish our destruction. . . . (I order) that all the forces in said Territory hold themselves in readiness to march, at a moment's notice, to repel any and all such invasion. — Territorial Gov. Brigham Young's proclamation, 1857

The first commander named for the U.S. Army expedition was Gen. William Harney. His biographer would later write that he "had fully determined, on arriving at Salt Lake City, to capture Brigham Young and the twelve apostles and execute them in summary fash- ion." But Harney would never go to Utah, for he was soon sent instead to quell unrest in Kansas.

He was replaced by Col. Albert Sidney Johnston, who was far away in Texas. So Johnston's Army of 2,500 — a third of the nation's entire Army at the time — would be crossing the Plains without him for most of the trip. The march also started late in the season; wagons were scattered in long trains. Officers didn't expect much opposition from Mormons to such a powerful force.

All of those were mistakes.

Should a collision take place between the good people of Utah and the detachment sent thither, the news of such an event would produce the most intense excitement throughout this vast confederacy, and the tide of public sentiment would set against us with tremendous force. — Utah congressional delegate John Bernhisel, warning Brigham Young to avoid a shooting war

Young indeed sought to avoid the shooting that Bernhisel warned would solidify public opinion against Mormons, but he also wanted to keep the Army away — and buy time for negotiations. So he sent militia to harass and slow the Army.

Porter Rockwell, a famous gunslinger, was the first to attempt to strike a blow for the Mormons. He and some militia attempted to stampede and steal a herd of Army mules near South Pass at Pacific Springs.

"He got away with them at first," historian William P. MacKinnon, who is writing a two-volume history on the war, told the modern-day caravan.