Europe in 1300
Northeastern Europe
Teutonic Knights
The Knights got here by way of a deal with the pope and the emperor whereby they were given these lands provided they conquered and converted the pagans who were living there, the Prussians. This they did over the course of the 13th century.
Especially after the union of Lithuania and Poland, the Teutonic Knights sought to battle against Poland to avoid being swallowed up. They failed. They hung on after the Battle of Grünwald in 1410 for another century, but the order dissolved itself when its grandmaster turned Lutheran in 1525.
Poland
Poland was an old duchy, formed about 250 years before when a Polish chieftain converted to Christianity and was made a duke. Poland vacillated between being a duchy and being a kingdom. Occasionally Poland vaulted into the limelight by means of a strategic marriage. During our course it was when the Polish house married into the French house of Anjou, always an extremely ambitious family.Lithuania
Lithuania in 1300 was still pagan, the last significant area of paganism in Europe. Lithuania was covered with deep forests and huge marshlands, and its people were long accustomed to fending off invaders by simply disappearing into the wilds until the foreigners left. Annual incursions by bands of Christian knights were already a tradition by 1300. It was striking news, therefore, when a Lithuanian king agreed in 1386 to convert to Christianity and marry the princess of Poland. This not only marked the end of paganism in Europe, it also united Poland and Lithuania into a significant power for a time. This story is much more complex (and interesting), but I'll leave it at this oversimplification.
Livonia
I should also mention the region known in the Middle Ages as Livonia, which consisted of modern Latvia, Estonia and northern Lithuania. It had been largely converted by a crusading order similar to the Teutonic Knights, known as the Sword Brothers. They united with the Knights in 1267 and so this region also belonged to the Teutonic Knights.