Relations with Other States Bulgarian interest in trade with the developing countries has increased considerably. In 1971 and 1972 the volume of trade with third world countries exceeded 316 million leva (for value of the lev--see Glossary) as opposed to 113.3 million leva in 1965. The Arab countries rank first in the amount of business conducted with Bulgaria. A considerable number of Bulgarian experts are also engaged in the construction of industrial enterprises in various developing countries. MEMBERSHIP IN REGIONAL AND INTERNATIONAL ORGANIZATIONS Regional Cooperation Military cooperation on a regional basis was secured for Bulgaria and its allies (the Soviet Union, East Germany, Hungary, Poland, Romania, and Czechoslovakia) in a multilateral alliance known as the Warsaw Pact. Albania, an original member, withdrew in 1968 (see ch. 16). Signed on May 14, 1955, in Warsaw, Poland, the pact was and remains Eastern Europe's answer to the challenges and security arrangements of the North Atlantic Treaty Organization (NATO). In one sense it seemed to provide legal grounds for the Soviet Union to keep its troops in east-central Europe as well as to secure the balance of military power in Europe, especially after West Germany joined NATO. In another sense it confirmed the Soviet Union's political and military hegemony in all of Eastern Europe. The organization has two main bodies--the Political Consultative Committee, which recommends general questions of foreign policy for member countries, and the High Command of United Armed Forces, which prepares military plans in time of war and decides troop deployments. Both bodies are located in Moscow, and all its senior ranking officials are Russians. Bulgaria has bilateral treaties of mutual aid with each other member of the Warsaw Pact. A multilateral agreement binds all the members to one another in general and to the Soviet Union in particular. Within Bulgaria Soviet officers serve as advisers at the division level and formerly served down to the regiment level. Others serve as instructors. Bulgaria was a charter member of COMECON in 1949. An economic alliance among Eastern European countries, COMECON is the counterpart to Western Europe's European Economic Community (commonly called the Common Market). Other members are the Soviet Union, Czechoslovakia, Hungary, Poland, Romania, and East Germany. Mongolia and Cuba, non-European countries, joined in June 1962 and July 1972, respectively. Albania joined in 1949 but withdrew in 1961.