Complex sentence: He studied at the University of Cambridge in the years leading up to World War II, spending spare time running messages for the Quakers in Nazi Germany, and working to smuggle Jewish people out of the country up to the outbreak of war.
Split into simpler sentences: He studied at the University of Cambridge in the years leading up to World War II and spent spare time running messages for the Quakers in Nazi Germany. He also worked to smuggle Jewish people out of the country right up until the outbreak of war.