Final answer:
Abraham Lincoln, the 16th U.S. President, guided the nation through the Civil War and issued the Emancipation Proclamation in 1863, focusing on preserving the Union and abolishing slavery.
Step-by-step explanation:
Abraham Lincoln was the 16th President of the United States and led the nation through its Civil War. Elected in 1860, and faced with the secession of southern states over issues surrounding slavery and states' rights, Lincoln's primary aim was to preserve the Union. His tenure saw pivotal actions such as the Emancipation Proclamation in 1863, which declared enslaved people in the Confederacy to be free, ultimately changing the character of the war from just unification to include the abolition of slavery as well.