On this day, November 29 1997, around 28,000 couples gathered at RFK Stadium (Washington, D.C.), for a satellite broadcasted “wedding” conducted by Sun Myung Moon of the Unification Church

Source: https://en.wikipedia.org/wiki/Unification_Church

"wedding" is in quotes because

The New York Times referred to a 1997 ceremony for 28,000 couples as a "marriage affirmation ceremony", adding: "The real weddings were held later in separate legal ceremonies."

See also this article from the 1997 BBC website: http://news.bbc.co.uk/2/hi/special_report/1997/unification_church/34821.stm

This is also the same Unification Church from the assassination of Japan's Shinzo Abe. In more recent news: Japan asks court to strip Unification church of religious status