Geopolitically, the Greece-Turkey system is crucial for containing the USSR to the south, both by sea and land. It controls, from the Black Sea, the Dardanelles Straits and the Aegean, the only maritime passage of the USSR (Russia) to the Eastern Mediterranean, the Middle East, and North Africa. On land, the two countries form a unified space, from the Balkans to Iran, cutting off the USSR's access to the Middle East. Together with Cyprus, the Greece-Cyprus-Turkey system constitutes the main support for Israel, the main bridgehead of the US in the region.