Oversea Arrivals to the U.S.

Due to the terrorist attack of September 11, 2001 oversea traveling to the U.S. dropped.  People also believed that the terrorist attack was due to overseas terrorism, “U.S. officials say their "working assumption" is that the attacks in New York and Washington are acts of "overseas terrorism." They say they cannot rule out additional attacks.” (U.S. Officials Say 'overseas Terrorism' Likely – CNN)

These statistics help to make us aware of historical events based on dates or major things that happened around this time.  For example during the war the unemployment rate went down because there were more jobs available.  The drop in oversea travel in 2001 was due to the historical event of a terrorist attack. 
"U.S. Officials Say 'overseas Terrorism' Likely - CNN." Featured Articles from CNN. 11 Sept. 2001. Web. 24 Jan. 2011. <http://articles.cnn.com/2001-09-11/us/overseas.terrorists_1_terrorist-osama-bin-attacks-officials?_s=PM:US>.