This question can refer to numerous wars. Here is a list of different wars you may be referring to:
1) World War I- The US abandon the policy of neutrality for multiple reasons. One of them was the German's use of unrestricted submarine warfare on ships containing American goods and citizens. The German's sank a British passenger ship, the Lusitania, that contained over 100 American citizens. These citizens were killed in this attack. Along with this, the United States also learned about Germany's attempt to make a secret alliance with Mexico in which Mexico would invade the US to prevent them from helping the Allied Powers. The US found out about this through the interception of the Zimmerman Telegram by the British. These two factors caused America to enter World War I.
2) World War II- The United States entered World War II after the Japanese military bombed the US military base called Pearl Harbor in Hawaii.
Maybe..... the signing of the constitution???
The Northern and Southern economies were very different in the decade prior to the Civil War.
Northern economy
At this time, the Northern economy was heavily influenced by industrialization. Northern cities focused predominantly on the development of manufactured goods thanks to the new organization systems and technological developments taking place during the middle of the 19th century.
Southern economy
The Southern economy was dominated by one cash crop, cotton. Cotton became "King" at this time, as the invention of the cotton gin increased the profit plantation owners could make off this product. This resulted in the Southern economy lacking in industrialization and transportation networks, making it completely different than the North.
Answer: I think it would be 3 correct me if I’m wrong:)
Explanation:
It gave the North a military advantage.