Complex sentence: After his graduation from high school, George studied art at the Académie Julian with Jean-Paul Laurens and others, until 1916, when World War I caused Joseph P. Herrick, ambassador at that time, to order all Americans to return home.
Split into simpler sentences: After his graduation from high school, George studied art at the Académie Julian. He stayed there, studying with Jean-Paul Laurens and others, until 1916, when World War I caused Joseph P. Herrick, ambassador at that time, to order all Americans to return home.