Conversation so far:
In what year did retirement take place for Lew Wallace?
Wallace resigned from the U.S. Army in November 1865 and briefly served as a major general in the Mexican army, before returning to the United States.
Where was Lew Wallace stationed when he retired?
On January 22, 1865, Grant ordered Wallace to the Rio Grande in southern Texas to investigate Confederate military operations in the area.

Question: What did he do for the military?
Self-contained rewrite: What did Lew Wallace do for the U.S. military?