<P> During the American Civil War (1861--1865), the Union referred to the United States of America and specifically to the national / federal / central government of 16th President Abraham Lincoln and the 20 free states and 4 border and slave states (some with split governments and troops sent both north and south), that supported it . The Union was opposed by 11 southern slave states (or 13, according to the Southern view and one western territory) that formed the Confederate States of America, or also known as "the Confederacy ." </P> <P> 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 . </P>

How many states were in the union during civil war