The flag of the United States of America from 1861 to 1863, with 34 stars for all the 34 states. The southern states were still represented in the number of stars in the flag because the Confederacy's declaration of secession from the Union was still considered illegal by the United States and President Abraham Lincoln. In 1863, a star was added to represent the new 35th state of West Virginia of the loyal northwestern counties of the seceded Commonwealth of Virginia, and in 1864, a 36th star for the new western state of Nevada (previously the Nevada Territory)
All of the Union's states provided soldiers for the United States Army (also known as the Union Army), though the border areas also sent tens of thousands of soldiers south into the Confederacy. The Border states were essential as a supply base for the Union invasion of the Confederacy, and Lincoln realized he could not win the war without control of them, especially Maryland, which lay north of the national capital of Washington, D.C.. The Northeast and upper Midwest provided the industrial resources for a mechanized war producing large quantities of munitions and supplies, as well as financing for the war. The Midwest provided soldiers, food, horses, financial support, and training camps. Army hospitals were set up across the Union. Most states had Republican Party governors who energetically supported the war effort and suppressed anti-war subversion in 1863–64. The Democratic Party strongly supported the war at the beginning in 1861 but by 1862, was split between the War Democrats and the anti-war element led by the "Copperheads". The Democrats made major electoral gains in 1862 in state elections, most notably in New York. They lost ground in 1863, especially in Ohio. In 1864, the Republicans campaigned under the National Union Party banner, which attracted many War Democrats and soldiers and scored a landslide victory for Lincoln and his entire ticket against opposition candidate George B. McClellan, former General-in-Chief of the Union Army and its eastern Army of the Potomac.
The war years were quite prosperous except where serious fighting and guerrilla warfare took place along the southern border. Prosperity was stimulated by heavy government spending and the creation of an entirely new national banking system. The Union states invested a great deal of money and effort in organizing psychological and social support for soldiers' wives, widows, and orphans, and for the soldiers themselves. Most soldiers were volunteers, although after 1862 many volunteered in order to escape the draft and to take advantage of generous cash bounties on offer from states and localities. Draft resistance was notable in some larger cities, especially New York City with its massive anti-draft riots of July 1863 and in some remote districts such as the coal mining areas of Pennsylvania.
Charleston Mercury Secession Broadside, 1860 - "The Union" had been a way to refer to the American Republic
In the context of the American Civil War, the Union is sometimes referred to as "the North", both then and now, as opposed to the Confederacy, which was "the South". The Union never recognized the legitimacy of the Confederacy's secession and maintained at all times that it remained entirely a part of the United States of America. In foreign affairs the Union was the only side recognized by all other nations, none of which officially recognized the Confederate government. The term "Union" occurs in the first governing document of the United States, the Articles of Confederation and Perpetual Union. The subsequent Constitution of 1787 was issued and ratified in the name not of the states, but of "We the People of the United States, in Order to form a more perfect Union ...". Union, for the United States of America, is then repeated in such clauses as the Admission to the Union clause in Article IV, Section 3.
Even before the war started, the phrase "preserve the Union" was commonplace, and a "union of states" had been used to refer to the entire United States of America. Using the term "Union" to apply to the non-secessionist side carried a connotation of legitimacy as the continuation of the pre-existing political entity.
Confederates generally saw the Union states as being opposed to slavery, occasionally referring to them as abolitionists, as in reference to the U.S. Navy as the "Abolition fleet" and the U.S. Army as the "Abolition forces".