Why did Lincoln decide to change his official show stand of slavery?

Lincoln decided to change his official stance on slavery primarily due to the moral imperative he felt to address the issue and the strategic necessity of preserving the Union during the Civil War. His Emancipation Proclamation in 1863 aimed to weaken the Confederacy by freeing enslaved people in rebelling states, thereby making the war about ending slavery. Additionally, he recognized that abolishing slavery could bolster the Union's war effort by allowing formerly enslaved individuals to join the military and contribute to the fight. Ultimately, this shift reflected a growing belief that the future of the nation depended on confronting and abolishing slavery.