Sources

Travel outbound of the U.S. from 1999 to 2018 obtained through U.S Department of Commerce.
Terrorist events around the world from 1999 to 2017 obtained through Global Terrorism Database at the University of Maryland.
Travel Advisory rankings from U.S Department of State - Bureau of Consular Affairs.
Destination Description - Safety and Security JSON file from U.S. Government's Open Data.
Twitter 136 posts with hashtags #travel AND #terrorism from Twitter available from June 2009 to April 2019.
A Survey from Gallup News Service published in June 2017 - Results based on telephone interviews conducted with a random sample of 1,009 adult.
Articles on terrorist attacks since 9/11