Congress passed the Militia Act of 1862 to address the urgent need for military support. This legislation allowed America's African-descent population to join the Union army and help save the Union. It had become an "indispensable military necessity." Shortly after President Abraham Lincoln signed the legislation on July 17, 1862, free men of color joined volunteer regiments in Illinois and New York. These men would later participate in some of the war's most notable campaigns and battles, including Antietam, Vicksburg, Gettysburg, and Sherman's Atlanta Campaign.