Final answer:
The Thirteenth Amendment, proposed by Congress on January 31, 1865, made slavery illegal throughout the United States, thereby abolishing the institution of slavery.
Step-by-step explanation:
On January 31, 1865, at President Abraham Lincoln's urging, Congress proposed the Thirteenth Amendment, which made slavery illegal throughout the United States. This amendment officially and permanently banned the institution of slavery and any form of involuntary servitude, except as a punishment for a crime where the party has been duly convicted. With the passage and ratification of the Thirteenth Amendment, slavery was abolished, impacting the lives of four million previously enslaved individuals by granting them freedom.