Complex sentence: In World War I, he was an infantry major with the IV Corps during the St. Mihiel offensive, and as a colonel, he later served with the III Corps throughout the Meuse-Argonne Offensive.
Split into simpler sentences: In World War I, he was an Infantry Major with the IV Corps during the Battle of Saint-Mihiel. As a Colonel, he later served with the III Corps throughout the Meuse-Argonne Offensive.