structural:reformatting
Union victory and aftermath

The causes of the war, reasons for its outcome, and even its name are subjects of lingering contention. The North and West grew rich while the once-rich South became poor for a century. The national political power of the slaveowners and rich Southerners ended. Historians are less sure about the results of postwar Reconstruction, especially regarding the second-class citizenship of the freedmen and their poverty.

Historians have debated whether the Confederacy could have won the war. Most scholars, including James M. McPherson, argue Confederate victory was possible. McPherson argues that the North's advantage in population and resources made Northern victory likely, but not guaranteed. He argues that if the Confederacy had fought using unconventional tactics, it would have more easily been able to hold out long enough to exhaust the Union. Confederates did not need to invade and hold enemy territory to win, but only to fight a defensive war to convince the North the cost of winning was too high. The North needed to conquer and hold vast stretches of enemy territory and defeat Confederate armies to win. Lincoln was not a military dictator and could fight only as long as the American public supported it. The Confederacy sought to win independence by outlasting Lincoln; however, after Atlanta fell and Lincoln defeated McClellan in the election of 1864, hope for a political victory for the South ended. Lincoln had secured the support of the Republicans, War Democrats, border states, emancipated slaves, and the neutrality of Britain and France. By defeating the Democrats and McClellan, he defeated the Copperheads, who had wanted a negotiated peace with the Confederacy.

Some scholars argue the Union held an insurmountable long-term advantage over the Confederacy in industrial strength and population. Confederate actions, they argue, only delayed defeat. Historian Shelby Foote expressed this view succinctly:

I think that the North fought that war with one hand behind its back.... If there had been more Southern victories, and a lot more, the North simply would have brought that other hand out from behind its back. I don't think the South ever had a chance to win that War.

A minority view among historians is that the Confederacy lost because, as E. Merton Coulter put it, "people did not will hard enough and long enough to win." However, most historians reject the argument. McPherson, after reading thousands of letters written by Confederate soldiers, found strong patriotism that continued to the end; they truly believed they were fighting for freedom and liberty. Even as the Confederacy was visibly collapsing in 1864–65, most Confederate soldiers were fighting hard. Historian Gary Gallagher cites General Sherman, who in early 1864 commented, "The devils seem to have a determination that cannot but be admired." Despite their loss of slaves and wealth, with starvation looming, Sherman continued, "yet I see no sign of let-up—some few deserters—plenty tired of war, but the masses determined to fight it out."

Also important were Lincoln's eloquence in rationalizing the national purpose and his skill in keeping the border states committed to the Union cause. The Emancipation Proclamation was an effective use of the President's war powers. The Confederate government failed to get Europe involved militarily. Southern leaders needed to get European powers to help break the blockade the Union had created around Southern ports. Lincoln's naval blockade was 95% effective at stopping trade goods; as a result, imports and exports to the South declined significantly. The abundance of European cotton and Britain's hostility to slavery, along with Lincoln's naval blockades, severely decreased any chance that Britain or France would enter the war.

Historian Don Doyle has argued that the Union victory had a major impact on world history. The Union victory energized popular democratic forces. A Confederate victory, on the other hand, would have meant a new birth of slavery, not freedom. Historian Fergus Bordewich, following Doyle, argues that:

The North's victory decisively proved the durability of democratic government. Confederate independence, on the other hand, would have established an American model for reactionary politics and race-based repression that would likely have cast an international shadow into the 20th century and perhaps beyond.

Scholars have debated what the effects of the war were on political and economic power in the South. The prevailing view is that the southern planter elite retained its powerful position in the South. However, a 2017 study challenges this, noting that while some Southern elites retained their economic status, the turmoil of the 1860s created greater opportunities for economic mobility in the South, than in the North.