I don’t know what timeline map you have, but it was for the expansion of American Democracy.
The United States first began developing nuclear weapons in 1939, during World War II, under the order of President Franklin Roosevelt. Motivation was the fear that US was engaged in a race with Nazi Germany to develop nuclear weapon. This project is best known as Manhattan Project.
Although John Cabot (ca. 1450-1499) established an English claim to the North American continent as early as 1497-1498, more than half a century elapsed before Englishmen turned their attention to the new lands.
