The answer to the question above is the potato.
The product that the Spanish Conquistadors found in the New World and took back to Europe that greatly affected the growth of the European population, especially among the lower classes was the potato.
1) The Platt Amendment declared Cuba a U.S. protectorate.
U.S. involvement in Cuba resulted from the U.S. defeat of Spain in the Spanish-American War of 1898. Cuba had to meet a series of conditions in order for U.S. troops to withdraw from Cuba.
2) Monroe Doctrine declared that an act by a European power in the Western Hemisphere would be considered a threat.
Proposed by Monroe in 1823? (check me on this) from lessons learned after the War of 1812 and continued British meddling in North America.
3) Roosevelt's Corollary set up the United States as a Latin American police force.
This was Roosevelt's famous "Speak Softly and Carry a Big Stick" policy. The world tour of the U.S. Navy's Great White Fleet is also a good example of the Roosevelt Corollary. U.S. troops were sent to various Latin American countries in the early 20th century (Nicaragua, Dominican Republic, Haiti, etc.) when U.S. business interests were threatened.
4) Panama Canal reduced time and expense of U.S. global trade by shortening shipping route between the Atlantic and the Pacific.
One of the most important engineering feats of the 20th century.
