During the American Civil War, the Union was the term used to refer to the camp formed by the northern states during the Civil War, and specifically to the national government of President Abraham Lincoln, made up of the 20 free states in favor of abolishing slavery and 5 border slave states that supported it. The Union was opposed by 11 southern slave states that had declared a secession to unite with each other to form the Confederacy.
The Union is also often referred to as "the North," both then and now, as opposed to the Confederacy's other name, "the South." The Union never recognized the legitimacy of secession and at all times maintained that it comprised the entire United States of America. In foreign affairs it was recognized by all other nations as the legitimate Government of the country.
Explanation:
Without doubt the great cause of the Civil War was the issue of slavery. Beginning with Vermont in 1777, most northern Ohio River states and the Mason-Dixon Line abolished slavery. These state jurisdictions enacted the first abolition laws throughout the "New World". Slavery in Massachusetts was abolished by the judiciary since the Constitution (also adopted in 1780) declared that all men have rights, therefore slavery was inapplicable. Emancipation in many free states was gradual: those who were slaves often remained slaves, yet the children of slaves were born free.
Most northerners recognized that slavery existed in the South and that the Constitution did not allow the federal government to intervene there. Most northerners favored a policy of gradual and compensated emancipation. After 1849, abolitionists rejected this and demanded that slavery end immediately and everywhere.The white abolitionist movement in the North was led by social reformers, especially William Lloyd Garrison, founder of the American Society Against Slavery, and writers like John Greenleaf Whittier and Harriet Beecher Stowe.
There were heated debates in Congress over laws like the 1850 Compromise, the Fugitive Slave Act (Abolitionists were outraged that the new law requires northerners to assist in the capture and return of runaway slaves), and the Kansas-Nebraska Act, that opened up the territories to slavery if local residents voted that way.
The Union Army was the ground force that fought for the Union during the Civil War. It consisted of the small United States Army (the regular army) augmented by a massive number of units supplied by the northern states, made up of volunteers as well as conscripts. The Union Army fought and ultimately defeated the Confederate Army during the war, which lasted from 1861 to 1865. Some 360,000 soldiers died and some 280,000 people were injured. The Union Army was led by General Ulysses S. Grant, who launched a war of attrition that would defeat General Robert E. Lee and end up presiding over the country between 1869 and 1877.