What is the 20 year return of the S&P 500?

Could you please elaborate on the long-term performance of the S&P 500 over a 20-year period? I'm curious to understand the average annualized return, taking into account the ups and downs of the market during this timeframe. Additionally, I'm also interested in knowing if there are any notable trends or factors that have contributed significantly to its overall performance over the last two decades.