Looking at Turkey first, NATO solidarity tops the list. NATO faces more threats in the southern region, along Turkey's borders, than anywhere else. Iran, Iraq, Syria, and the Caucasus. It has a growing strategic relationship with another long-term American ally, Israel, and it controls access to the Black Sea. The successful exploitation and security of Caspian oil and natural gas reserves will certainly involve the transport of energy resources through Turkey, either overland or through the Bosporus, or both.
Turkey is a Muslim democratic country.
The successful melding of Islam with a democratic, Western-oriented government serves as a model for many other nations in the region. With regard to Greece, the strategic importance of the country has increased because of events in the Balkans over the last 10 years. Greece is certainly the most stable and economically viable country in that region. Greece's role in the region's development will grow even more as Balkan countries continue to struggle with their future. Access to the port of Thessaloniki and the natural terrain features connecting Greece with the Former Yugoslav Republic of Macedonia and Kosovo are key to keeping the logistic lines of communication open to U.S. and other NATO troops.