Not Tsunade but the Elders, it was not her who created the exams.
This is true, but who decides who will increase in rank...I'm pretty sure The Hokage has something to do with that. The elders aren't the one's who created the chunin exams neither. After the 3rd Ninja World War, allied ninja villages agreed to hold the exams together at the selected village that would host the exam, so villages could improve and strengthen their relationships. Another advantage is that ninja that took the exam might attract clients who are interested in hiring them. The exam is a test not only of strength, but information gathering abilities, survival skills, and adhering to guidelines. Those who have all of these qualities are grouped together into predetermined fights, watched by a council that decides who becomes a Chunin and who does not. While the winners are able to proceed to fight the next opponent, it is aptitude, rather than winning, that is evaluated to determine whether a candidate is promoted. This way even one who loses his or her first match can become a Chunin as evidenced by Shikimaru's promotion while he surrendered to Temari in the first round.
