The American Revolution, which occurred from 1776 to 1783, was responsible for the formation of the country. However, it was the Civil War, which occurred from 1861-1865, that really set the course for how the nation would be run. It was the Civil War that determined whether or not the United States would truly become its own indivisible nation. It also determined whether or not the United States would continue being the country with the largest number of slaves, which was ironic, since the country was founded on the idea that all men are created equal and entitled to be free.
Eleven southern states (Alabama, Arkansas, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas and Virginia) declared their Ordinances of Secession from the United States and formed the Confederate States of America, also known as "the Confederacy".
Twenty-Two mostly-Northern states (California, Connecticut, Delaware, Indiana, Illinois, Iowa, Kansas, Maine, Minnesota, Massachusetts, Michigan, New Hampshire, New Jersey, New York, Ohio, Oregon, Pennsylvania, Vermont, Rhode Island, Wisconsin) formed the Union.
When the North won the Civil War, slavery was abolished in the United States and the country became unified. However, about 625,000 people were killed in the Civil War. The combined death totals from all other wars the United States has fought in since is about that amount. So, the Civil war was a destructive, bloody battle. In fact, it was the most destructive conflict for the entire century from the Napoleonic wars of 1815 to World War I, which took place in 1914.
The original cause of the Civil War was disputes between the slave states and the free states about whether or not the federal government should have the power to prohibit slavery in non-state regions (territories). Abraham Lincoln, a Republican, became President of the United States in 1860. He was against slavery in the territories, which led to 7 states ceding from the Union. They created the Confederate States of America in protest of the anti-slavery movement. The Northern state and Lincoln's administration, however, worried that democracy would cease if they were to legitimize the secession of those states. They didn't want the country to split into several other countries, creating opposing factions.
The first battle of the Civil War took place when the Confederate army fired on the Fort Sumter federal garrison on April 1, 1861 at Charleston Bay. They wanted to claim the fort as their own, and they succeeded in doing so. That caused Lincoln to order militia men into service to stop them. Soon, 4 more states joined the Confederate side. A battle line stretching about 1,200 miles from Missouri to Virginia existed by the time 1861 was over. At that time, many battles had already been fought. Some of them were in the following areas; Manassas Junction in Virginia; Wilson's Creek in Missouri; Cape Hatteras in North Carolina ; Port Royal in South Carolina.
That last battle allowed the Union army to create a blockade, preventing the Confederacy from receiving any help from other nations by water.
It was in 1862 that the bulk of the Civil War began. The following major battles were fought during that year; Shiloh in Tennessee; Gaines' Mill, Second Manassas and Fredericksburg in Virginia; Antietam in Maryland
Originally, the North only wanted to bring the Union back to its original state with as few battles as possible, but the war was in full force by 1864. They wanted to obliterate slavery and the concept of the Old South, giving way to freedom. President Lincoln gave his famous Gettysburg Address with that in mind when he was honoring fallen Union soldiers.
Between 1862 and 1865 the Union didn't have much luck getting past the Northern Virginia army of Robert E. Lee. However, in 1864 General Ulysses S. Grant came to the area and took control of the Union army in the region. That led to the battles of the Wilderness, Spotsylvania, Cold Harbor and Petersburg.
In April of 1865, at Appomattox, Grant finally defeated Lee. Around that same time, Union armies gained victories in several Appalachian Mountain regions. General William Tecumseh Sherman destroyed the southern economies in South Carolina and Georgia between 1864 and 1865. General George Thomas, meanwhile, fought and won the battle of Nashville, destroying the Tennessee branch of the Confederate troops.
Most of the major Confederate armies had surrendered to the Union by 1865. The war ended on May 10, 1865, when the union captured Confederate President Jefferson Davis, who was on the run in Georgia at the time. At that time, the rebuilding process began, but it took a long time for the nation to become fully unified and slavery-free.
The data below comes from Original Documents from the National Archives:
The data below comes from Ancestry.com: