What significant action did Abraham Lincoln take during his presidency?

Abraham Lincoln is best known for issuing the Emancipation Proclamation during his presidency, which was a critical turning point in American history. Signed on January 1, 1863, this executive order declared the freedom of slaves in the Confederate states, effectively changing the legal status of millions of enslaved people. It shifted the focus of the Civil War from merely preserving the Union to also addressing the moral imperative of ending slavery.

The Emancipation Proclamation provided a clear union war policy that also aimed to weaken the Confederacy, as the workforce in agricultural economies would be disrupted. Furthermore, it set the stage for the eventual passage of the Thirteenth Amendment, which formally abolished slavery in the United States.

The other actions listed, while significant in their own rights, are not associated with Lincoln in the same capacity. Signing the Declaration of Independence occurred long before Lincoln's presidency, and the New Deal was part of Franklin D. Roosevelt's administration aimed at economic recovery during the Great Depression. The Gettysburg Address, although an important speech by Lincoln, did not have the same immediate and direct impact on the status of slavery as the Emancipation Proclamation did.