The Emancipation Proclamation made it legal for African Americans to free themselves by helping to save the Union in the American Civil War. Abraham Lincoln wrote that his Proclamation was “warranted by the Constitution upon military necessity.” It was necessary to secure the help of America’s African descent population in order to save the Union, which was Lincoln’s paramount objective.

African Americans made up over 10 percent of the Union or Northern army even though they were prohibited from joining until July 1862, 15 months into the war. They comprised 25 percent of the Union navy, yet, only 1 percent of the Northern population was African American. Clearly overrepresented in the military, African Americans played a decisive role in the Civil War.

The first African descent combatants were sailors. They served on every classification of ship in the navy’s inventory. The Militia Act of 1792, which banned the enlistment of African Americans in the army, did not apply to the navy. Consequently, there were free men of color serving in the navy when the Civil War began in April 1861.

After word got to Washington in July 1862 that Union Gen. George McClellan’s army was in full retreat suffering a humiliating defeat, Congress passed the Militia Act of 1862. It had become an “indispensable military necessity” to call on America’s African descent population to help save the Union. A few weeks after President Lincoln signed the legislation on July 17, 1862, free men of color joined volunteer regiments in Illinois and New York. Such men would go on to fight in some of the most noted campaigns and battles of the war to include Antietam, Vicksburg, Gettysburg, and Sherman’s Atlanta Campaign.

On Sept. 27, 1862, the first regiment to become a United States Colored Troops (USCT) regiment was officially brought into the Union army. All the captains and lieutenants in this Louisiana regiment were men of African descent. The regiment was immediately assigned combat duties, and it captured Donaldsonville, La., on Oct. 27, 1862. Before the Emancipation Proclamation was issued, two more African descent regiments from Kansas and South Carolina would demonstrate their prowess in combat.

After the Emancipation Proclamation was issued on Jan. 1, 1863, the War Department publicly authorized the recruiting of African Americans. The first regiment raised with such authority was the 54th Massachusetts Infantry. (Leading many to report that it was the first African descent regiment.) By the end of 1863, Gen. Ulysses S. Grant viewed the African descent population armed with the Proclamation as a “powerful ally.”

African Americans fought in every major campaign and battle during the last two years of the war earning 25 Medals of Honor. USCT regiments captured Charleston, the Cradle of Secession, and Richmond, the capital of the Confederacy. Lincoln recognized their contributions. He declared, “Without the military help of the black freedmen, the war against the South could not have been won.” And without the Emancipation Proclamation, these soldiers and sailors would have had little reason to fight for the Union.

Hari Jones is the curator of the African American Civil War Museum in Washington, D.C.