150-Year Anniversary ยท June 1862
Having taken command after Seven Pines, Robert E. Lee resolved to drive McClellan from the gates of Richmond. On June 26 he opened the Seven Days Battles at Mechanicsville, and on June 27 he struck the isolated Union corps north of the Chickahominy at Gaines' Mill.
Gaines' Mill saw the largest Confederate attack of the war to that point. After a day of bloody repulses, a coordinated evening assault broke the Union line, forcing the Federals back across the river in the first clear Confederate victory of the campaign.
The defeat convinced McClellan to abandon his advance and retreat toward the James River, surrendering the initiative he had held since spring. Lee had seized the momentum that would carry the war into Maryland by autumn.
Gaines' Mill was the bloodiest of the Seven Days. The rest of that eastern campaign is framed on the American Civil War overview.