Complex sentence: After fighting in the American Revolutionary War and learning that his service and labor meant nothing to those in charge, he became a member of the Jeffersonian Republican Party (otherwise known as the Democratic-Republican Party) in response to the day's ruling Federalist Party.
Split into simpler sentences: After fighting in the American Revolutionary War, he began to believe that his service and labor meant little to those in charge. He soon became a member of the Jeffersonian Republican Party (otherwise known as the Democratic-Republican Party) in response to the day's ruling Federalist Party.