<span>The territorial gain made by the United States as a result of the Spanish-American War are the Philippines, Puerto Rico, and Guam moved toward becoming domains of the United States as a major aspect of the terms of the Treaty of Paris that authoritatively finished the Spanish-American War of 1898.</span>
Well without a description om shooting in the dark. But id assume that the answer is Trench Warfare. Since A- was around since contact with Native Americans and largely popular in North America. B- Only was used and discovered in WW2. And C- was used but was largely frowned upon and condemned by both sides.<span />
Ok so when the americans moved west, they built plantations and needed slaves for the plantations. In the east, however, the northern half wanted to free all of them.
1 is probably your best bet since your talking about unit 1 or period 1 which was focuses on irrigation