The departure of Yugoslavs seeking work began in the 1950s, when individuals began slipping across the border illegally. In the mid-1960s, Yugoslavia lifted emigration restrictions and the number of emigrants, including educated and highly skilled individuals increased rapidly, especially to West Germany. By the early 1970s 20 percent of the country's labor force or 1,1 million workers were employed abroad. The emigration was mainly caused by force deagrarization, deruralization, and overpopulating of larger towns. The emigration contributed to keeping the unemployment checked and also acted as a source of capital and foreign currency. The system was institutionalized into the economy. From 1961 to 1971, the number of guest workers from Yugoslavia in West Germany increased from 16,000 to 410,000.