The Yippies were one of many protest groups in the 1960s that protested the Vietnam War. It was founded by several people, most notably Abbie Hoffman and Jerry Rubin. The Yippies were an offshoot of the much larger, college based Students for a Democratic Society (SDS). The founding of the organization really was jump-started by the Democratic Convention in Chicago in which they organized a free music festival and called it the "Festival of Life".
As time passed, a character unique to the Yippies formed. The Yippies became known as a very left organization. There acts were a tad radical, such as their threat to put drugs in Chicago's water supply. Abbie Hoffman even led a rally earlier, in which he claimed to perform an exorcism of the Pentagon and make it levitate, with the help of a mass of protesters.
However, the Yippies' radical ideals made many government officials take the Yippies' threats seriously. This caused a great deal of tension, which led to the many outbreaks of violence, especially at the Democratic Convention of 1968 in Chicago. It also put the Yippies in a negative light in most of the nation.