I know comparatively little about the history of Central and Eastern Europe. I picked up quite a lot about the Roman Empire up to about 80 AD in the course of learning Latin, but my history lessons at school were concerned much more with Western Europe and to a lesser extent the Americas.
I had a very good friend in Germany – he taught History and English – and when we stayed with him one Summer, he spent one totally engrossing evening laying out for us the threads of history which showed how a purely pragmatic political decision made by the Emperor Otto sometime round the 1100's (the creation of the Prince-Bishops) led to Hitler and the Third Reich. I wish I could remember the whole of it, but all that remains in my memory now are the barest outlines. He got cancer and died in 1999, and I still miss him. He was a lovely man and a good friend, but his life was dogged by some of the cruellest misfortune.
Also, during a visit to the Baltic States, I learned that Lithuania had a short-lived Empire covering a large area in the north of central Europe, sometime in the 1400's IIRC. However, I know very lttle, and nothing systematic, about the history of Poland, Hungary, the Czech Republic, Slovakia, Romania, Bulgaria, the Balkan States and the Ottoman Empire.