End of the dot com bubble.
https://en.m.wikipedia.org/wiki/Stock_market_downturn_of_2002
But it happened mostly in 2000:
https://en.m.wikipedia.org/wiki/Dot-com_bubble
And coincidentally 9/11
The September 11 attacks also contributed heavily to the stock market downturn, as investors became unsure about the prospect of terrorism affecting the United States economy.