More specifically, YouTube has a practical monopoly on publishing and promoting user-generated video in the US.
Anybody can generate video and a great many do. Promoting your video to millions of viewers is a bit more challenging, though can clearly be done wihtout YouTube: https://www.lifewire.com/videos-that-went-viral-before-youtu...
This doesn't even get into the really early viral videos like the charcoal briquettes lit with liquid oxygen, or the massive viewership of the comet Shoemaker-Levy 9 impact way back in the day.
