What was the sole purpose of why the u. s. joined world wars

The United state was always ready for any outcome but not until 1916 went a French boat was sinked which was unarmed, but the primary purpose of united state to join the world was the German resumption of submarine attacks on passenger and merchant ships in 1917 made president Wilson decides to lead the United state into world war.

Explanation:

answer; andrew jackson approved nullification by signing it into law,and john calhoun opposed it saying it was unconstitutional;