I believe what you're looking for is The Great Depression
The correct answer to this open question is the following.
Should the US have become an empire?
No of course not, because that would have been in direct opposition to the elevated ideas expressed by the United States Founding fathers when they created the US Constitution and established the new form of government during the Constitutional Convention held in Philadelphia, Pennsylvania in the summer of 1787.
Nevertheless, as it happens in the history of the nations, there were Presidents that under the idea of the Manifested Destiny tried to expand the US territory waging war, invading, and supporting imperialistic ideals, as was the case of President James Polk. It was the time of the Mexican-American War when the United States got the territories of California, Arizona, and New Mexico, Other Presidents had similar foreign policies.
How long could the US have maintained an isolationist policy toward the world?
Basically, the US developed the concept of isolationism during two important times in modern history. First, at the beginning of World War I. US President Woodrow Wilson tried to maint the foreign policy of neutrality. Years later, at the beginning of World War II, US President Franklin D. Roosevelt tried to do the same. In both cases, after terrible events, both presidents decided to enter the war.
Answer:
D. The two countries signed an agreement to prevent accidental military clashes.
The US made South africans into slaves
Answer:
Ideally, Hernan Cortes should try to establish peaceful alliances with the Native Americans, as hard as this might be. The problem is that the Aztecs were at war with many other tribes, and it would have been incredibly hard for Cortes to form an alliance among them.
Another problem is that Cortes and his Spanish companions were bringing diseases for which the Native Americans had no antibodies, so it is likely that many Native Americans would have died no matter what Cortes and the Spaniards did.