It was a United States naval officer/ historian, also known to be a propagandist to expansion, named Alfred Thayer Mahan who wanted to expand the extent of capacity of the United States and its navy. He wrote “The Influence of Sea Power upon History”. It stated his idea that the countries with the biggest navies and greater sea power over others who could govern the world. With his principles, and knowing that US had at that time the elements of the capability to expand its greatness, he created strategies based on commerce trading and coastal defense to support the Manifest Destiny. Manifest Destiny states that it is the United States who was the ones who were destined to expand across North America.
FDR was the one who led America through the Great Depression, even tho it was the actual start of WWII that got us out of it. He also got us through the majority of WWII until he died near the end and the position was taken over by his Vice President, Truman.
