What was ONE important thing that Abraham Lincoln did?

Abraham Lincoln is widely recognized for his significant role in the abolition of slavery in the United States. The Emancipation Proclamation, issued by Lincoln in 1863, declared that all slaves in the Confederate states were to be set free. This pivotal action not only changed the landscape of American society but also paved the way for the eventual passage of the Thirteenth Amendment, which formally abolished slavery throughout the entire country. Lincoln's leadership and determination during the Civil War eras emphasized his commitment to human rights and equality, marking him as a crucial figure in American history.

The other choices, while important in their own contexts, do not directly relate to Lincoln's contributions. Lincoln was not involved in the establishment of National Parks or the creation of the Federal Reserve, which occurred later. He also did not sign the Civil Rights Act, as that legislation was passed in 1964, long after his presidency.