The world is not an equal place, and some places are a lot more unequal than others.
A national political border can have incredible significance; an abstract line separating neighboring peoples, economies, even life expectancies. Using GDP per capita as an indicator (sourcing the most recent Central Intelligence Agency data), the wealth divide between these four pairs of countries is vast ... even though they geographically sit side by side.
Kuwait and Iraq
Difference in GDP per capita: $38,300
United States and Mexico
Difference in GDP per capita: $34,200
Brunei and Malaysia
Difference in GDP per capita: $34,200 (tied with U.S.- Mexico)
North Korea and South Korea
Difference in GDP per capita: $30,000