George B. McClellan in the context of "George Armstrong Custer"

The state of New Jersey in the United States provided a source of troops, equipment and leaders for the Union during the American Civil War. Though no major battles were fought in New Jersey, soldiers and volunteers from New Jersey played an important part in the war, including Philip Kearny and George B. McClellan, who led the Army of the Potomac early in the Civil War and unsuccessfully ran for President of the United States in 1864 against his former commander-in-chief, Abraham Lincoln.

The U.S. state of West Virginia was formed out of western Virginia and added to the Union as a direct result of the American Civil War (see History of West Virginia), in which it became the only modern state to have declared its independence from the Confederacy. In the summer of 1861, Union troops, which included a number of newly formed Western Virginia regiments, under General George McClellan drove off Confederate troops under General Robert E. Lee at the Battle of Philippi in Barbour County. This essentially freed Unionists in the northwestern counties of Virginia to form a functioning government of their own as a result of the Wheeling Convention. Before the admission of West Virginia as a state, the government in Wheeling formally claimed jurisdiction over all of Virginia, although from its creation it was firmly committed to the formation of a separate state.

After Lee's departure, western Virginia continued to be a target of Confederate raids. Both the Confederate and state governments in Richmond refused to recognize the creation of the new state in 1863, and thus for the duration of the war the Confederacy regarded its own military offensives within West Virginia not as invasion but rather as an effort to liberate what it considered to be enemy-occupied territory administered by an illegitimate government in Wheeling. Nevertheless, due to its increasingly precarious military position and desperate shortage of resources, Confederate military actions in what it continued to regard as "western Virginia" focused less on reconquest as opposed to both on supplying the Confederate Army with provisions as well as attacking the vital Baltimore and Ohio Railroad that linked the northeast with the Midwest, as exemplified in the Jones-Imboden Raid. Guerrilla warfare also gripped the new state, especially in the Allegheny Mountain counties to the east, where loyalties were much more divided than in the solidly Unionist northwest part of the state. Despite this, the Confederacy was never able to seriously threaten the Unionists' overall control of West Virginia.

The eastern theater of the American Civil War consisted of the major military and naval operations in the states of Virginia, West Virginia, Maryland, and Pennsylvania, the national capital in Washington, D.C., and the coastal fortifications and seaports of North Carolina. The interior of the Carolinas were considered part of the western theater, and other coastal areas along the Atlantic Ocean were part of the lower seaboard theater.

The eastern theater was the venue for several major campaigns launched by the Union Army of the Potomac to capture the Confederate capital of Richmond, Virginia; many of these were frustrated by the Army of Northern Virginia, a division of the Confederate States Army, commanded by General Robert E. Lee. President Abraham Lincoln responded by seeking a general to match Lee's boldness, and successively appointed Major General Irvin McDowell, George B. McClellan, John Pope, Ambrose Burnside, Joseph Hooker, and George G. Meade to command his principal eastern armies.

Henry Wager Halleck (January 16, 1815 – January 9, 1872) was a senior United States Army officer, scholar, and lawyer. A noted expert in military studies, he was known by a nickname that became derogatory: "Old Brains". He was an important participant in the admission of California as a state and became a successful lawyer and land developer. Halleck served as the General-in-Chief of the Armies of the United States from 1862 to 1864, and then became Chief of Staff for the remainder of the war when Ulysses S. Grant was appointed to that position.

Early in the American Civil War, Halleck was a senior Union Army commander in the Western Theater. He commanded operations in the West from 1861 until 1862, during which time, while the Union armies in the East were repeatedly defeated and held back, the troops under Halleck's command won many important victories. However, Halleck was not present at those battles, and his subordinates earned most of the recognition. The only operation in which Halleck exercised field command was the so-called siege of Corinth in the spring of 1862, a Union victory which he conducted with unnecessary caution, which allowed the Confederate force to escape. Halleck also developed rivalries with several of his subordinate generals, such as Grant and Don Carlos Buell. In July 1862, following Major General George B. McClellan's failed Peninsula Campaign in the Eastern Theater, Halleck was promoted to general-in-chief. Halleck served in this capacity for about a year and a half.

Presidential elections were held in the United States on November 8, 1864, near the end of the American Civil War. Incumbent President Abraham Lincoln of the National Union Party easily defeated the Democratic nominee, former General George B. McClellan, by a wide margin of 212–21 in the electoral college, with 55% of the popular vote. For the election, the Republican Party and some Democrats created the National Union Party, especially to attract War Democrats.

Despite some intra-party opposition from Salmon Chase and the Radical Republicans, Lincoln won his party's nomination at the 1864 National Union National Convention. Rather than re-nominate Vice President Hannibal Hamlin, the convention selected Andrew Johnson of Tennessee, a War Democrat, as Lincoln's running mate. John C. Frémont, who had been the Republican nominee in 1856, started to run as the nominee of the new Radical Democratic Party, with War Democrat John Cochrane as Frémont's running mate; the new party criticized Lincoln for being too moderate on the issue of racial equality, but Frémont and Cochrane withdrew from the race in September and their new party dissolved. The Democrats were divided between the Copperheads, who favored immediate peace with the Confederacy, and War Democrats, who supported the war. The 1864 Democratic National Convention nominated McClellan, a War Democrat, but adopted a platform advocating peace with the Confederacy, which McClellan rejected, although his running mate George H. Pendleton wrote it. While the Confederacy seemed to have survival potential in summer 1864, it was visibly collapsing by election day in November.

Pinkerton is an American private investigation agency and security company established around 1850 in the United States by Scottish-born American cooper Allan Pinkerton and Chicago attorney Edward Rucker as the North-Western Police Agency, which later became Pinkerton & Co. and finally the Pinkerton National Detective Agency. At the height of its power from the 1870s to the 1890s, it was the largest private law enforcement organization in the world. It is currently a subsidiary of Swedish-based Securitas AB.

Pinkerton became famous when he claimed to have foiled the Baltimore Plot to assassinate President-elect Abraham Lincoln in 1861. Later, Lincoln's general-in-chief, George B. McClellan, hired Pinkerton to conduct espionage against the Confederacy and provide Confederate troop estimates during the American Civil War. As such, Pinkerton and his agency are sometimes seen as the forerunners of the United States Secret Service.