The emblem on your button was used on US Army Staff-Officer buttons from 1832 to 1902. However, your button's back is the "self-shank" type, and no US Military buttons had a self-shank back. Also, that version of self-shank back dates from the early-20th-Century, after the 1832-to-1902 US Officer button was discontinued. Lastly, your button's construction is called a "false 3-piece" button. It is made to resemble the 3-piece type, but it actually does not have a separate rim/ring holding the button's front and back together. No American-made US Army buttons are the "false 3-piece" type. Your button is believed to be an imitation manufactured in the early-1900s for use on Veterans uniforms after the actual 1832-to-1902 version was no longer being made.