Some stocks within an index may be commodity stocks, with any fluctuations in the market having the potential to affect the index price.
Events such as natural disasters or pandemics would negatively impact an index market by affecting the impacted country’s economy.
Economic events and meetings such as central bank rate decisions, NFPs, trade agreements and employment indicators.
When a company's stock is added or removed from a stock index, the prices can see a shift.
Important company news, such as new leadership, a merger or release of financial results.