Geostrategically, the Greece-Turkey system is of vital importance for containing the USSR to the South, both by sea and by land. It controls, from the Black Sea, the Straits of Dardanelles and the Aegean, the only maritime passage of the USSR (Russia) to the Eastern Mediterranean, the Middle East, and North Africa. By land, the two countries form a unified space, from the Balkans to Iran, blocking the USSR's access to the Middle East. Together with Cyprus, the Greece-Cyprus-Turkey system constitutes the main support for Israel, the primary bridgehead of the USA in the region.