Battle of Gaines's Mill

Battle context

The Battle of Gaines's Mill was the third of the Seven Days Battles and proved decisive in determining the outcome of the Union's Peninsula Campaign. Lee renewed his assault on the Union right flank after the inconclusive engagement at Beaver Dam Creek, targeting Fitz John Porter's V Corps, which was isolated north of the Chickahominy River. The Confederate attack, the largest of the war at roughly 57,000 men across six divisions, ultimately pressed Porter's position and demonstrated Lee's intent to maintain relentless offensive pressure on McClellan's army. The engagement inflicted substantial casualties on both sides — nearly 8,000 Confederate and over 7,300 Union — reflecting the intensity of the fighting. Within the broader Seven Days sequence, Gaines's Mill contributed to the cumulative operational shock that compelled McClellan to abandon his advance on Richmond and shift the Army of the Potomac's base, effectively ending the Peninsula Campaign's bid to capture the Confederate capital.