John Sheldon Doud Eisenhower was a United States Army officer, diplomat, and military historian. He was the son of President Dwight D. Eisenhower and First Lady Mamie Eisenhower. His military career spanned from before, during, and after his father's presidency, and he left active duty in 1963 and then retired in 1974. From 1969 to 1971, Eisenhower served as United States Ambassador to Belgium during the administration of President Richard Nixon, who was previously his father's vice president and also his daughter-in-law's father. As a military historian, Eisenhower wrote several books, including The Bitter Woods, a study of the Battle of the Bulge, So Far from God, a history of the Mexican–American War and Yanks: The Epic Story of the American Army in World War I .