On Dec. 21, 1866, a year and a half after Gen. Robert E. Lee and Gen. Ulysses S. Grant ostensibly closed the book on the Civil War’s final chapter at Appomattox Court House, another soldier, Capt. William Fetterman, led cavalrymen from Fort Phil Kearny, a federal outpost in Wyoming, toward the base of the Big Horn range. The men planned to attack Indians who had reportedly been menacing local settlers. Instead, a group of Arapahos, Cheyennes and Lakotas, including a warrior named Crazy Horse, killed Fetterman and 80 of his men. It was the Army’s worst defeat on the Plains to date. The Civil War was over, but the Indian wars were just beginning.

These two conflicts, long segregated in history and memory, were in fact intertwined. They both grew out of the process of establishing an American empire in the West. In 1860, competing visions of expansion transformed the presidential election into a referendum. Members of the Republican Party hearkened back to Jefferson’s dream of an “empire for liberty.” The United States, they said, should move west, leaving slavery behind. This free soil platform stood opposite the splintered Democrats’ insistence that slavery, unfettered by federal regulations, should be allowed to root itself in new soil. After Abraham Lincoln’s narrow victory, Southern states seceded, taking their congressional delegations with them.

Never ones to let a serious crisis go to waste, leading Republicans seized the ensuing constitutional crisis as an opportunity to remake the nation’s political economy and geography. In the summer of 1862, as Lincoln mulled over the Emancipation Proclamation’s details, officials in his administration created the Department of Agriculture, while Congress passed the Morrill Land Grant Act, the Pacific Railroad Act and the Homestead Act. As a result, federal authorities could offer citizens a deal: Enlist to fight for Lincoln and liberty, and receive, as fair recompense for their patriotic sacrifices, higher education and Western land connected by rail to markets. It seemed possible that liberty and empire might advance in lock step.