My Auxiliary Sciences of History teacher said since the forging of the Donation of Constantine ( http://en.wikipedia.org/wiki/Donation_of_Constantine ) When Europe was split in two. The Papal Western and the Byzantine Eastern

Around the time that the Byzantine Empire started to decline so did the rest of Eastern Europe. By the seventeenth century Russia was considered to be technologically and economically behind the West of Europe. I would say that this is because they remained much more feudal and in addition had no colonies like Spain or the Netherlands or any of the other powers.

After Russia was modernized by Peter the great and then Catherine the great it managed to compete as a great power until its political collapse during the Communist Revolution. Even though during and especially after World War 2 Russia was among the top two or three strongest countries it was severely mismanaged in terms of collectivization of farming and production of goods. So tl;dr I would say that Eastern Europe definitively became poorer than Western Europe was in the 30s.

I am saying this from what I read out of an older textbook, so it may not be entirely accurate. There were a few key differences in the East and West. First of all, in the 14th century and onward, while serfdom in Western Europe was becoming less common, in Eastern Europe it was growing, with increasingly harsher demands on the serfs, due to a number of reasons, including landlords cutting towns, which often were a key market for serfs extra goods to sell, out of business by selling directly to foreigners. This was due to a number of reasons, especially the Black Death. While landlords in the West had not succeeded in placing greater demands on their serfs to compensate for their losses, those in the East largely did. This continuation and expansion of serfdom slowed commercial growth in the East significantly. The Mongol occupation of Russia also played a role in the divide.