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What Military Action Started the American Civil War? [The Complete Answer]

Written by Everett Bledsoe / Fact checked by Brain Bartell

what military action started the american civil war

The American Civil War is one of the many wars worth knowing about. If you do not know a lot about this war, it is a good idea to get started by reading how it started. Do that using our article right here. We will answer, “What military action started the American Civil War?” and provide you with other relevant information on Civil War history. So, make sure you read this until the very end!

The American Civil War (US Civil War)


How did the Civil War start?

The war began in 1861, following decades of tension between the Northern and Southern states. But let’s backpedal a bit and look at the background leading up to the causes of the Civil War.

In the mid-19th century, the United States was experiencing remarkable growth, which led to a wealth gap between the nation’s Northern and Southern regions.

While the North established a solid manufacturing industry, the South depended on large-scale farming using enslaved people’s labor. Setting the inhumane nature of slavery aside, this became a problem when abolitionist sentiment grew and Southerners were worrying that the essence of their economy was threatened.

When the Kansas-Nebraska Act passed in 1854 to permit new territories to “access” slavery, the North opposed and in doing so, formed the Republican Party. They refused to let slavery extend into the Western regions.

However, in 1857 the Supreme Court confirmed the legality of slavery through Dred Scott’s case. This led to the raid at Harper Ferry by abolitionist John Brown two years later. Conflict bottled, wherein Southerners were convinced that the Northerners were doing this to negate the South’s economy.

After Abraham Lincoln’s (anti-slave) election in 1860, the 7 Southern states seceded from the US and this was what started the Civil War.

Note: The two sides of the war were: the Confederates and the Union.

Consider watching this Youtube video on “How Slavery Caused the American Civil War”.

The American Civil War Begins…


  • When Lincoln took office (March 1861), Confederates threatened the Union’s Fort Sumter, the federal-held in South Carolina.
  • A month later (April 1861), Lincoln directed a fleet to resupply Sumter. Then the Confederates fired the first shots.
  • Sumter’s commander surrendered after two days and the fort switched hands.
  • Four more Southern states joined the Confederacy.
  • 35,000 Confederate soldiers pushed a number of the Union Federals to retreat to Washington D.C. This is called the First Battle of Bull Run or the First Manassas.
  • Lincoln called for 500,000 more Federal recruits.


  • General McClellan led the Union’s Army of Potomac up the peninsula between the James River and the York and captured Yorktown in May.
  • But the Confederate’s joint forces drove McClellan’s army back between June 25 and July 1 and Lincoln withdrew the army to Washington.
  • The joint forces moved Northwards and split up: a half led by Lee and the other half led by Jackson.
  • Union troops struck Jackson’s troops on August 29.
  • Lee’s troops returned the hit the next day, shooing the Union back to Washington.
  • McClellan struck back at Lee in Maryland on September 14, pushing them back to defense along Antietam Creek.
  • On September 17, the Battle of Antietam broke out. Casualties were 12,410 Union Federals and 13,724 Confederates.
  • Having lost the Battle of Antietam, the Confederates retreated to Virginia.
  • McClellan was replaced by Ambrose E. Burnside, who led troops to attack Lee’s troops on December 13 but lost and was then replaced by Joseph Hooker.
  • Lincoln issued a preliminary Emancipation Proclamation using the Union’s win at Antietam to free enslaved people in the rebellious states following January 1, 1863. As a result, a bulk of the South’s labor forces were cut off and the public opinion shifted to support the Union.
  • Up to 186,000 black soldiers joined the Union’s army.
  • On May 1, 1863, Lee’s forces launched a surprise attack, forcing Hooker’s men to retreat to Chancellorsville. In the Battle of Chancellorsville, the Confederates, despite winning, lost 22% of their troops, while the Union lost 15% (~17,000 men).
  • In June, Lee was attacked again, by Gettysburg. The two sides fought for three days but Lee lost 60% of his men and failed to push into the Union’s center.
  • In July 1863, the Union took Vicksburg (Mississippi).
  • Then, they won another battle at Chickamauga Creek, Georgia.
  • In November, thanks to their expansion in September, the Union’s army won the Battle of Chattanooga.

1864 – 1865

  • The Union federals took Atlanta in September and Savannah in December.
  • The Union took Columbia and Charleston of South Carolina in mid-February.
  • The Union captured most of North Carolina in April.
  • Lee’s men ultimately surrendered at the Appomattox Court House.
  • Unfortunately, the Union lost their leader Lincoln in April (He was assassinated).
  • The last of the Confederates surrendered at Durham Station, ending the Civil War.

Here is a crash course video of the US Civil War that you might want to watch!


1. What were the first 7 Southern states that seceded from the US, kickstarting the war?

Texas, South Carolina, Florida, Mississippi, Alabama, Georgia, and Louisiana were the first seven Southern states that withdrew or seceded from the US.

2. What were the 4 later Southern states that joined the US Confederates?

The four states were Virginia, Arkansas, North Carolina, and Tennessee. They all joined the confederates after the Fort Sumter victory.

3. What were the 3 Southern states that “stood from the sidelines?”

Missouri, Kentucky, and Maryland were the three states that did not secede from the US. But there was Confederate sentiment and sympathy among the citizens.

4. Who assassinated Abraham Lincoln?

John Wilkes Booth assassinated Abraham Lincoln. He was a Maryland native who sympathized with the Confederates. He intended to kidnap Abraham Lincoln and hold him hostage until all the prisoners of the Confederacy were released. But he ultimately shot Lincoln and fled. Booth was killed by Union’s men after 12 days.


There you have it; the complete answer to, “What military action started the American Civil War?” We hope that you found this article helpful. Was there anything that surprised you? Leave your thoughts with us in the comments below.

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