Before 1973, Watergate was simply the name of the apartment and office complex in Washington, D.C., that housed the Democratic National Committee headquarters.
After that headquarters was robbed and wiretapped by President Nixon's confederates, Watergate had a new meaning. Not much later, so did the suffix -gate, which came to mean "usually political scandal often involving the concealment of wrongdoing."
By the end of the 1970s, we had Koreagate (agents of the South Korean government were alleged to be trying to buy influence in the U.S. Congress) and Hollywoodgate (the president of Columbia Pictures was suspended for forging checks and then reinstated before the Securities and Exchange Commission had finished its investigation into the matter).
More recent -gates have included Monicagate, Troopergate, and Climategate.