Economically, Bulgaria still looks to the Soviet Union for foreign aid and preferential trade treatment. The rapid pace with which Bulgaria has moved toward industrialization is primarily owing to Soviet assistance. Raw materials critical to Bulgaria's economy are supplied by the Soviet Union and, with Soviet aid, the country has been able to construct many large industrial enterprises. Estimates in 1967 put the number of Soviet specialists in Bulgaria at 5,000, and the number has probably increased. The renewal of a five-year agreement for 1971 through 1975 would serve to increase further the Soviet share of trade in Bulgaria. Relations with Other Communist States Bulgaria's relations with Czechoslovakia, East Germany, Hungary, Poland, and Romania are largely governed by a series of bilateral and multilateral treaties of friendship and cultural cooperation and by military and economic alliances. The alliances are the Warsaw Pact and COMECON. Relations with the other two communist states of Eastern Europe, Albania and Yugoslavia, have usually followed Soviet initiatives toward those countries. Quite naturally, Bulgaria's major concerns in foreign affairs have dealt with relations among the states of the Balkan Peninsula and particularly with adjacent states. Romania, its northern neighbor, is a member of COMECON and the Warsaw Pact but has often appeared to be a reluctant member and since the early 1960s has stressed nationalism rather than Marxist internationalism, causing Bulgaria, with its strong Soviet orientation, to tread lightly in bilateral relations for fear of offending the Soviets. Nevertheless, the Bulgarians and Romanians have drawn closer together, probably because both countries see benefits that might accrue from Balkan cooperation and believe that such cooperation should in no way disturb the Soviet Union. In the early 1970s relations appeared to be particularly good: there were frequent meetings between leaders and government ministers, and a plan to cooperate in the building of a huge hydroelectric project on the Danube River between the two countries was announced.