Afghanistan has been called "the graveyard of empires." While disputes about the validity of the term continue, the fact is that the country has been a battleground for empires. From ancient times until today, the country has been invaded by what is present-day India, the Greeks, Muslims of the Rashidun caliphate, Mongols led by Genghis Khan, Persians, and Sikhs. More recently, the British Empire, the Soviet Union, and NATO led by the United States have had a go at establishing a presence in the nation. Why is Afghanistan so important? According to military tacticians, any entity controlling Afghanistan has a...