Your button's backmark is the key to correctly time-dating it. "AM Button Co Newark NJ" means the American Button Company, which began making uniform buttons (military, railroad, etc) in 1901. Its button-making factory burned in 1917 and the company ceased to exist in 1920. My info-source is the book "American Military Button Makers And Dealers; Their Backmarks & Dates" by William F. McGuinn and Bruce S. Bazelon.