What triggered a Civil War between the Union and the Confederates?

The answer generally revolves around slavery and a difference in opinion on the role and spread of slavery throughout America. There are nuances within this though, with issues of arguments over states rights vs the federal governments, economic considerations, as well as actions taken by individuals such as the Dred Scott Case, Tom Brown's action and the election of Lincoln. The eventual trigger is Six States leaving the Union and the Confederates opening fire on Fort Sumter.

The American civil war was triggered by deep seated tensions over slavery, states’ rights and political power. Some of the key events that lead up to the war included:

Slavery and expansion: The North and South were divided over whether slavery should expand into their newly acquired territories. The South wanted to maintain and expand slavery whilst the North wanted to limit or abolish it.

The election of Abraham Lincoln: Lincoln was a republican who opposed the expansion of slavery and won the presidency. The Southern states saw his victory as a threat to their way of life.

Attack on Fort Sumter: The immediate trigger was the Confederate attack on Fort Sumter, a Union fort in South Carolina. This marked the official beginning of the war, as Lincoln called for troops to suppress the rebellion.

The American Civil War, which erupted in 1861, was one of the most defining and tragic episodes in United States history. At the heart of this conflict between the Union (the North) and the Confederacy (the South) were deep-rooted political, economic, and social tensions, but it was the issue of slavery—its expansion, its morality, and its role in American society—that served as the central trigger. While multiple factors played a role, slavery was the flashpoint that ultimately made compromise impossible.

Slavery had been part of American life since colonial times, but by the mid-19th century, it had become a fiercely divisive issue. The Southern economy was heavily dependent on slavery, especially in its agricultural sector, where cotton, tobacco, and sugar plantations relied on enslaved labour. In contrast, the North was industrialising rapidly and moving away from an agricultural economy. Many Northerners came to view slavery as morally wrong and economically backward. Although not all Northerners were abolitionists, the growing anti-slavery sentiment created increasing hostility between the two regions.

The question of whether slavery should be allowed to expand into the western territories of the United States was particularly contentious. The Missouri Compromise (1820) and the Compromise of 1850 were attempts to maintain a balance between free and slave states, but these temporary solutions began to crumble as new states were added. The Kansas-Nebraska Act of 1854, which allowed settlers in those territories to decide whether to permit slavery, led to violent confrontations in what became known as “Bleeding Kansas.” This act overturned the Missouri Compromise and demonstrated that legislative efforts to contain the crisis were failing.

Political divisions mirrored the regional split. The once-dominant Democratic Party fractured along sectional lines, while the newly formed Republican Party—founded in opposition to the expansion of slavery—gained popularity in the North. The election of Abraham Lincoln in 1860 was the final spark. Although Lincoln had no intention to abolish slavery where it already existed, his firm stance against its expansion was unacceptable to many in the South. Fearing the loss of political and economic power, and believing their way of life was under threat, eleven Southern states seceded from the Union, forming the Confederate States of America.

Secession itself was a revolutionary act that made conflict almost inevitable. The Union saw the secession as illegal and unconstitutional, a direct threat to the survival of the United States. Lincoln refused to recognise the Confederacy and was committed to preserving the Union at all costs. When Confederate forces attacked Fort Sumter in April 1861, the Civil War began in earnest.

Other factors also contributed to the war: economic differences between an industrial North and an agrarian South, debates over states’ rights versus federal authority, and cultural divisions between the two regions. However, these were often closely intertwined with slavery. For example, Southern states claimed they were fighting for their right to self-govern—but that right primarily involved maintaining slavery.

In conclusion, while the Civil War was influenced by a range of political and economic factors, the core trigger was slavery—particularly its expansion into new territories and its role in shaping national identity. The failure of compromise, the polarisation of politics, and the deep moral divide between North and South made war unavoidable. The Civil War was not just a conflict over territory or governance, but a profound struggle over the values on which the United States would continue to be built.