BTW, it was originally going to be a campaign song for Timothy Leary!
In early 1969, John Lennon and his wife, Yoko Ono, held nonviolent protests against the Vietnam War, dubbed the Bed-ins for Peace. In May, during the Montreal portion of the bed-in, counterculture figures from across North America visited Lennon, including American psychologist Timothy Leary, an early advocate of LSD, whom Lennon admired. Leary intended to run for Governor of California in the following year's election and asked Lennon to write him a campaign song based on the campaign's slogan, "Come Together – Join the Party!". The resulting chant was only a line long: "Come together and join the party". Lennon promised to finish and record the song, and Leary later recalled Lennon giving him a tape of the piece, but the two did not interact again.