Throughout the modern era, there have been striking contrasts between the histories, economies, and politics of Eastern and Western Europe. After World War II, those differences became especially obvious with the Soviet led Warsaw Pact forces poised on one side of the Elbe River and the Western NATO alliance on the other. As so often in history, the underlying basis for these differences has been geography.
First of all, Europe's latitude lies quite far north. For example, Rome, Italy is about as far north as Chicago, Illinois. However, it has a much warmer climate, especially in the winter. This is because Western Europe gets the moderating effects of a warm current known as the South Atlantic Drift and warm sea breezes coming across the Mediterranean from North Africa. Eastern Europe is too far inland to benefit much from either of these effects, and thus has more extremes in climate, especially in the winter.
However, the critical difference between Eastern and Western Europe has to do with waterways. Western Europe has an abundance of navigable rivers, coastlines, and harbors along the Atlantic Ocean and the Mediterranean, North, and Baltic Seas. In the High Middle Ages, these fostered the revival of trade and the rise of towns, a money economy, and a middle class opposed to the feudal structure dominated by the nobles and Church.
Kings also opposed the nobles and the Church, so the middle class townsmen provided them with valuable allies and money. With this money, kings could buy two things. First of all, they could raise mercenary armies armed with guns to limit the power of the nobles. Secondly, they could form professional bureaucracies staffed largely by their middle class allies who were both more efficient since they were literate and more loyal since they were the king's natural allies and dependant on him for their positions. As a result, kings in Western Europe were able to build strong centralized nation-states by the 1600's.
Eastern Europe, in stark contrast to Western Europe, provided practically a mirror image of its historical development before 1600. Being further inland compared to Western Europe hurt Eastern Europe's trade, since the sea and river waterways vital to trade did not exist there in such abundance as they did in Western Europe.
Factors limiting trade also limited the growth of a strong middle class in Eastern Europe. This meant that kings had little in the way of money or allies to help them against the nobles. That in turn meant that peasants had few towns where they could escape the oppression of the nobles. Therefore, strong nobilities plus weak, and oftentimes elective, monarchies were the rule in Eastern Europe before 1600. At the same time, the nobles ruled over peasants whose status actually was sliding deeper into serfdom rather than emerging from it.
However, there was one geographic factor that favored Eastern Europe's rulers after 1600. That was the fact that Eastern Europe is next to Western Europe. As a result, some influence from the West was able to filter in to the East. In particular, Eastern European rulers would emulate their Western counterparts by adopting firearms, mercenary armies, and professional bureaucracies. As a result, they were able to build strongly centralized states in the 1600's and 1700's. This was especially true in three states: Austria-Hungary (the Hapsburg Empire), Brandenburg-Prussia in Germany, and Russia.
However, the lower incidence of towns and a strong middle class has continued to hamper the development of Eastern European states in the modern era, since rulers there have had to build their states with less of the strong foundation of a money based economy, basing their states on less developed agricultural economies. While the strong middle class in Western Europe would provide the impetus for further developments in the West, notably the emergence of democracy and the Industrial Revolution, these two things have had a harder time taking root in Eastern Europe, making its overall political and economic development more difficult.