Harry S Truman did a lot of things before he went into politics. After high school, he became a timekeeper at a railroad station. After that job, he went to be a clerk at a bank ("Truman:HST Biography"). He joined the Missouri National Guard in 1905. He went back home and worked on the family farm for 11 years (Truman).
After managing his family farm, Harry S Truman went to France as an artillery battery commander in World War I. When he got back from World War I, he married Elizabeth Virginia Wallace in 1919. They went on to have one kid, Mary Margaret. She was born in 1924 (Truman).
After the war, Harry S Truman opened a men's clothing store with one of his friends. That lasted from 1919-1922, but then Depression started to settle in a little, and they didn't get enough business ("Truman:HST Biography). He decided to go for a different occupation after that.
In 1922-24, Harry S Truman entered politics as a Democrat. He became the judge of Jackson county, Missouri. Then he became the presiding judge of the county court in 1926-1934. With the help of Thomas J. Pendergast, Harry S Truman got elected to the Senate in 1936. He was reelected in 1940 and 1944. While being a senator, he was an avid supporter of the New Deal. One of the cases that he dealt while he was in Senate was the waste from the war effort. In fact, he was the chairman of that committee.
Harry S Truman as First Lieutenant in World War I
http://www.electriceggplant.com/davidmccullough/images/photos/Truman-79-24.jpg