"The terror attacks of September 11, 2001 had an immediate and substantial impact on international travel worldwide. The attacks induced substitution away from air travel generally and caused a shift in the preferences of travelers for particular destinations. The United States in particular experienced an immediate and precipitous drop in arrivals of international visitors, particularly from those flying in from overseas. The initial drop in arrivals immediately following 9/11 in part reflected widespread concern about the safety of international air travel. Economic factors most likely also played a role in reducing travel to the United States in the aftermath of 9/11. Between 2001 and 2002, for example, the global economy experienced a recession that reduced demand for air travel generally. In addition to safety concerns and deteriorating economic conditions, the perception that U.S. visa policy became more restrictive in the wake of 9/11 may also have negatively impacted arrivals. Such perceptions prompted concern within the travel industry that the United States was becoming a less attractive travel destination and was damaging its image abroad."