What event had the biggest impact to tourism growth and why?

There are a number of factors that impacted the decrease of tourism growth after September 11 attacks in 2001. These include:

- Reduction of travel demand: The September 11 terrorist attacks caused an immediate drop in travel demand by almost 20% globally. This was in part due to safety and security concerns, with air travel falling even further (60%). Some countries and territories experienced much steeper drops.

- Reduction in flights and travel capacity: Many airlines, including major carriers such as American Airlines and United Airlines, slashed their flight schedules due to the reduced travel demand. This significantly decreased the number of seats available for leisure and business travel.

- Travel advisories and restrictions: In response to the September 11 attacks, governments worldwide issued travel advisories or restrictions, warning their citizens against travel to certain regions or countries. These advisories discouraged many travelers and impacted tourism bookings in affected areas.

- Economic slowdown and uncertainty: The aftermath of the September 11 attacks resulted in economic slowdown globally. This also reflected in the tourism sector, as businesses scaled back on travel expenditure and leisure travelers postponed their trips due to economic uncertainty.