The American Civil War (1861-1865) was the nation's deadliest conflict, killing almost 600,000 combatants and an unknown number of civilians. The conflict pitted the Union against the Confederate States of America, or the Confederacy, a breakaway alliance of 11 southern states that seceded from the Union over the issue of slavery.

For years, the subject of why the Civil War was fought has been a source of dispute and disagreement, although many historians agree that slavery was the major and irrevocable cause of the war. Slavery was a system of forced labor that exploited millions of Africans and African Americans for the benefit of white planters, merchants, and politicians in the South. Slavery was also a social institution that upheld white supremacy and racial discrimination, denying enslaved people their basic human rights and dignity.

Slavery was deeply embedded in the Southern economy, culture, and identity, and any threat to its existence was perceived as a threat to the Southern way of life. The North and the South had different views on slavery and its expansion into the new territories acquired by the United States. The North, which had a more diversified and industrialized economy, had largely abolished slavery by the early 19th century and supported the efforts of abolitionists who wanted to end slavery everywhere.

The South, which relied heavily on cotton production and enslaved labor, resisted any attempts to limit or interfere with slavery and demanded that slavery be protected and extended into the western lands. The conflict over slavery became more intense and violent in the decades leading up to the Civil War, as evidenced by events such as the Missouri Compromise (1820), the Nullification Crisis (1832-33), the Mexican-American War (1846-48), the Compromise of 1850, the Kansas-Nebraska Act (1854), the Dred Scott decision (1857), John Brown’s raid on Harpers Ferry (1859), and the election of Abraham Lincoln (1860).

Lincoln’s victory in 1860, without a single Southern electoral vote, convinced many Southerners that they had no future or voice in the Union. They feared that Lincoln and his Republican Party would abolish slavery and destroy their rights and interests. Between December 1860 and June 1861, 11 Southern states seceded from the Union and formed their own government, with Jefferson Davis as their president. They declared that they were fighting for their independence, sovereignty, and self-determination. However, they also made it clear that they were fighting to preserve and defend their peculiar institution of slavery, which they considered essential to their social order and economic prosperity.

The Union, led by Lincoln, fought to preserve the nation as one indivisible entity, and to uphold the principles of democracy and federalism. Lincoln initially stated that his main goal was not to abolish slavery, but to save the Union. However, as the war progressed, he came to realize that slavery was the root cause of the rebellion and that ending slavery was necessary to secure a lasting peace. He proclaimed the freedom of all enslaved people in the rebel states in 1862, which was known as the Emancipation Proclamation.

In 1863, he delivered his famous Gettysburg Address, which defined the war as a struggle for human equality and democracy. In 1865, he supported the passage of the Thirteenth Amendment, which abolished slavery throughout the United States.

The Civil War was not only a military conflict but also a moral crusade. It was fought over the fundamental question of whether slavery was right or wrong, and whether it should be allowed or abolished in a free and democratic society.

The war resulted in the liberation of four million enslaved people, but it also left a legacy of bitterness, division, and trauma that still haunts America today. The war challenged Americans to live up to their ideals of liberty and justice for all and to confront their history of racism and oppression.

The war also inspired Americans to strive for a more perfect union and to continue working for civil rights, social justice, and racial reconciliation.