American Military History, Volume 1 by Richard W. Stewart

After Appomattox the Army had to muster out over a million volunteers and reconstitute a regular establishment that had languished during the Civil War when bounties and short enlistments made service in the volunteers more profitable. There were operational commitments to sustain during and after the transition, some an outgrowth of the war just ended and others the product of internal and external situations that could not be ignored. Whereas the prewar Army of the 1850s was essentially a frontier Army, the postwar Army became something more. To defense of the frontier were added military occupation of the southern states, neutralization of the Mexican border during Napoleon's colonial enterprise under Maximilian, elimination of a Fenian (Irish Brotherhood) threat to Canada in the Northeast, dispersion of white marauders in the border states, and a growing mission of coastal defense. But the mission of pacifying the frontier consumed much of the interest and attention of large numbers of Army officers and men in the years between the Civil War and the Spanish-American War.