The battle of Gettysburg on July 1-3, 1863, was the greatest loss of life on both sides of the Civil War in a single battle. Lee, confident after his successes at Chancellorsville, was set on a decisive defeat of the Union Army as part of a northern invasion. The battle would prove otherwise. Union forces outnumbered the Confederate Army by 25 percent. Confederate forces suffered 28,063 casualties and Union forces suffered 23,049 killed, wounded, or captured – nearly a third of all troops engaged in the battle. It is considered the most costly battle in US history, both in loss of life and loss of generals. The battle was crippling on both sides, and to the nation as a somber significance of how costly the war had become and the magnitude of the casualties on both sides. While the Union declared victory of the battle, it is still debated by some historians.