Between 1861 and 1865 the violent struggles of the Civil War extended into the Western Territories, where they were complicated by the involvement of the Indians. The Confederate leaders had planned to annex a corridor from the Rio Grande in Texas to the California coast. Thus they would have had a pathway to the Pacific Ocean, areas rich in minerals, new territory for the expansion of slavery, and valuable military stores and equipment. They soon found that the land was more difficult to conquer than they had anticipated. The people of the Western Territories for the most part remained loyal to the Union, and the Confederate vision of empire failed to materialize.

The emphasis in this book is on the Union campaigns against the Confederates and the Indians who sought to take advantage of the confusion of the Civil War. Yet it is also shown that the Western Territories came of age as a result of the conflict. When the Confederate invasion had been repelled, the Union leaders undertook vigorous campaigns for extermination or settlement of the Indians on reservations. Arizona, Colorado, New Mexico, and Utah all acquired their present boundaries and patterns of state government during the Civil War period.