A recent epidemiological study found that businesspeople who travel internationally on business are much more likely to suffer from chronic insomnia than are businesspeople who do not travel on business  International travelers experience the stresses of dramatic changes in climate, frequent disruption of daily routines, and immersion in cultures other than their own, stresses not commonly felt by those who do not travel
Thus, it is likely that these stresses cause the insomnia
Most international travel for the sake of business occurs between countries with contiguous borders.