The Continental Navy was created by George Washington in 1775 to protect the American colonies from attacks by the British. At the end of the Revolutionary War, the Continental Navy was disbanded. However, American merchant ships were under continuous attacks by North African pirates so the Department of the Navy was created by Congress in April 1798. Also, after the American Revolution, the British refused to leave American territory along the Great Lakes and continued to attack American merchant ships. This led to the War of 1812.
The most important event was obviously the American Civil War from 1861-1865. This led to the 14th Amendment which defined a citizen as "any person born or naturalized in the US." The 13th Amendment abolished slavery, and the 15th Amendment prohibits denying the right to vote to someone because of their race.
Other key events include the Louisiana Purchase, the Texas Revolution, The Spanish-American War, the War of 1812, the purchase of Alaska, the Mexican Cession, the Indian Wars, and the California Gold Rush.
Like I said, the right to vote was extended to all male citizens by the 15th Amendment. Women were not given the right to vote until the 19th Amendment was passed in 1920.
Which war is the question stating?
The Yalta Conference happened at the end of World War II and encompassed Great Britain (Churchhill), Russia (Stalin), and the United States (FDR) coming together to demand the complete surrender of German forces.
