Between 1933 and 1939, Germany expanded and strengthened its trade connections with a number of Eastern European countries to a point where their economic expansion became dependent on trade with Germany, making it the dominant economic power in the region. By 1939, the year the Second World War began in Europe, Germany was the largest trading partner of the four countries listed; this was also true of Czechoslovakia in 1937, Poland in 1938, and the Soviet Union in 1940, although the share of total exports to Germany from these countries was lower.
German influence increases in the Second World War
To consolidate its power in the region, Germany exported its high-quality industrial products to these countries and paid above-market prices to import raw materials and agricultural produce. Following the outbreak of the war, Germany invested more into the farming sectors of the four countries listed, to the point where they were economically subordinate and considered satellite extensions of the German economy. The demand for agricultural imports from these countries impeded their industrialization and prevented them from developing their industries that could compete with Germany. Three of the countries listed would side with the Axis powers as the war escalated. At the same time, Yugoslavia was quickly annexed, and a puppet government was installed, continuing the agricultural supply to Germany.
Post-war difficulties
Following the war, the four listed countries eventually fell within the Soviet sphere of influence (though Yugoslavia to a lesser extent than the other three), and the dominance of agricultural sectors led to difficulties, as new communist governments attempted to take their economies in a more industrialized direction. The socialist economic systems required the agricultural means of production to be publicly owned (collectivized); however, many rural landowners were unwilling to part from their land; especially in Bulgaria. These factors exacerbated the delaying effect that Germany had had on these countries' industrialization in the 1930s, contributing to the economic imbalances that emerged between Europe's Eastern and Western Blocs in the decades that followed.