 He missed the 1917 national championships, but was still named as the top high hurdler to both the All-American athletic team and the All-American collegiate team of the year.After the 1917 season Simpson joined the United States Army and attended the officers' training camp at Fort Sheridan; he became a lieutenant and track and field instructor for the 91st Division.He resumed hurdling after World War I was over, winning both the high hurdles and the low hurdles at the 1919 Inter-Allied Games in Paris; in the low hurdles he had lost to his own cousin, William Sylvester, in the American tryouts for the meet, but defeated him at the Games themselves.