On November 13, 1890, troops moved into South Dakota, a military movement that would result six weeks later in the Wounded Knee Massacre. The president sent soldiers to South Dakota, the largest movement of troops since the Civil War, in the midst of a midterm election campaign that looked bad for his party.

In 1890, Republican president Benjamin Harrison was facing a revolt in the midterms. The Republicans had risen before the Civil War as the party of ordinary farmers and workers, and had fought the Civil War to take control of America out of the hands of the nation’s wealthy slave owners. But after the war, Republicans had gradually swung behind the nation’s rising industrialists—men like Andrew Carnegie and J. D. Rockefeller—and propped up their industries with tariff walls that enabled them to keep consumer prices high. Voters, who hated the tariffs, increasingly backed the Democrats, who promised to lower them. Democrats had won the House of Representatives in 1874, and in 1884, Grover Cleveland became the first Democrat elected to the White House since the 1850s. Horrified Republicans had pulled out all the stops in 1888 to reclaim the government for their party.

In the 1888 election, they tapped large donors to fill the Republican war chest, then used the money to flood newspapers with pro-tariff arguments, warning that the Democrats were radicals who would destroy the economy, and promising that Republicans themselves would “reform” the tariff. But while Republicans’ strategy won the House of Representatives, it didn’t work for the presidency: Cleveland garnered about 100,000 more votes than the Republican candidate, Benjamin Harrison. So Republican operatives swung the election in the Electoral College, striking a backroom deal with the New York delegation to win an electoral victory. When the pious Harrison mused that Providence had given him the win, one of his operatives grumbled, “Providence hadn’t a damn thing to do with it. A number of men were compelled to approach the penitentiary to make him President.”

Harrison’s men recognized that they could not continue to hold power under the current system. So they rigged it. They admitted six new western states to the Union, the largest bulk admission of states since the original thirteen. In 1889, they split the huge Territory of Dakota into two parts—North Dakota and South Dakota—and added both to the Union, along with Washington and Montana. They fully expected the new states to vote Republican: when Montana went Democratic, they claimed the vote was fraudulent and replaced the Democrats with Republicans. In 1890, they added Wyoming and Idaho, moving so fast in the latter case that they had to call for volunteers to write a constitution that voters approved only months later. It was unclear that any of these western states even had enough people in them to justify statehood, but Republicans insisted the forthcoming 1890 census would prove that admitting them had been warranted. Administration men boasted that the admission of the new states would guarantee Republican control of the Senate and the Electoral College for the foreseeable future.

With this security in place, party leaders actually raised, rather than lowered, tariff rates just before the November election. They insisted that stronger protections for business would help workers by making the economy boom.

Furious voters gave Democrats a 2:1 majority in the House of Representatives. Republicans continued to hold the Senate, but by only four seats, and three of those senators were from states that had just gone Democratic. The survival of Republican control of the Senate came down to one man: the Senator from South Dakota.

In 1890, Senators were still chosen by state legislatures, and at first South Dakota Republicans claimed to have won the election. But almost immediately, that became doubtful: ballot boxes had been broken open and results altered. The Republicans had to make their case for South Dakota legislators to choose a Republican Senator between November and January, when the legislature met.

Right then, on November 13, with control of Congress hanging on South Dakota’s senatorial seat, President Harrison ordered 9,000 troops to South Dakota—the largest mobilization of the army since the Civil War—to protect settlers against an Indian “uprising,” an uprising that Harrison and his advisors knew had claimed no lives and no property. Army officers scoffed at the deployment, telling the president to feed the starving Lakota instead.

As the troops moved into South Dakota, the story of the election was eclipsed by what was happening on the ground. When panicked Lakota fled their reservations, army officers used both negotiations and troop movements to try and corral them back toward the government agencies at the heart of each reservation, where the army could keep an eye on them. But those negotiations went bad on the Standing Rock Reservation in the northern part of the new state when Indian police tried to bring Lakota leader Sitting Bull to the agency and ended up murdering him and much of his band. Wounded survivors ran south to take shelter with famous negotiator Sitanka at the Cheyenne River Reservation. But their arrival panicked Sitanka’s band and the entire group headed south across the middle of the state toward the Pine Ridge Reservation, to hole up with another Lakota leader on good terms with the army, the elderly Red Cloud.

It was several days before the troops cornered Sitanka’s people on the evening of December 28. Cold and tired, their leader sick with pneumonia, the band surrendered and moved, as ordered, to Wounded Knee Creek on Pine Ridge Reservation, where they were headed anyway. As night fell, the soldiers placed rapid-fire guns on the hills surrounding the camp. During the night, Colonel James Forsyth, a senior commander far more experienced with paperwork than with western fighting, took over the troops, and the following day he ordered the Indians disarmed.

As the soldiers took the few weapons the Indians had, three soldiers and a Lakota man began to struggle over a valuable gun, and it fired into the air. “Fire! Fire on them!” Forsyth shouted. In minutes, half the surrendering Lakota and 25 soldiers lay dead. The artillerymen began lobbing shells at the people escaping in both directions along the road and at those running into the ravine that lay behind the encampment. Over the next two hours, soldiers hunted down and killed all the Lakota they could find, riding them down and shooting them at point blank range as they tried to escape. Some women were murdered after they had run two miles from the campsite; one of those killed was a four month old infant who was shot from such close range gunpowder was imbedded in his skin.

In the end, about 270 Lakota and 30 soldiers died at the Wounded Knee Massacre. The Republicans did not hold the South Dakota senate seat. After weeks of balloting, it went to an Independent who caucused with the Democrats.