<P> The first fatalities of the war happened during the Baltimore Civil War Riots of Thursday / Friday, April 18 - 19th, 1861, and the single bloodiest day of combat in American military history occurred during the first major Confederate invasion of the North, just above the Potomac River, near Sharpsburg, Maryland, (Washington County) at the Battle of Antietam, on 17 September 1862 . Preceded by the pivotal skirmishes at three mountain passes to the east in the Battle of South Mountain, Antietam, though tactically a draw, was strategically enough of a Union victory in the second year of the war to give 16th President Abraham Lincoln the opportunity to issue the Emancipation Proclamation, which declared slaves in the Confederacy (but not those in semi-loyal border slave states like Maryland, Delaware, Kentucky, and Missouri) to be free . </P> <P> Later, in July 1864, the Battle of Monocacy near Frederick, Maryland in the third and last major Southern invasion, was also fought on Maryland soil . Monocacy was a tactical victory for the Confederate States Army but a strategic defeat, as the one - day delay inflicted on the Confederates by General Lew Wallace cost General Jubal Early his chance to capture the Union capital of Washington, D.C. during the attack on the outlying northwestern fortifications near Fort Stevens, witnessed by President Lincoln himself . </P> <P> Across the state, nearly 85,000 citizens signed up for the military, with most joining the Union Army . Approximately one third as many enlisted to fight for the Confederacy . The most prominent Maryland leaders and officers during the Civil War included Governor Thomas H. Hicks who, despite his early sympathies for the South, helped prevent the state from seceding, and Confederate General George H. Steuart, who was a noted brigade commander under Robert E. Lee . </P> <P> The end of the war would bring the abolition of slavery in Maryland, with a new constitution voted in 1864 by a small majority . Animosity against Lincoln would remain, and Marylander John Wilkes Booth would assassinate President Lincoln in April 1865, crying "sic semper tyrannis" as he did so . </P>

What side did maryland fight on in the civil war
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