The 1862 battle at Antietam put an end to

the Confederate threat to the Union capital.

Explanation:

The Antietam battle was a battle centred in Maryland that ended General Lee's first invasion of the North. General Lee, was a best known commander in the Americas. He had hoped to defeat the union in their own land and force the North to give up the war. The war enabled the union to repel the first confederate invasion of the North.

answer; ///i believe that the correct answer is (a) the great depression