War is Peace, and we Have Always been at War With Eastasia.
While the HRE and France were natural enemies, it was fairly common for certain French rulers to desire to rule both and attempt to add their own territory to the empire. Strangely enough, the emperor often accepted such threats to his power.
With the threat of the mongol horde growing ever closer in the fifteenth century, the powerful states to the east in the Holy Roman Empire declared their desire to end the threat once and for all by overruning the horde and pushing their armies into the seas on the other side.
The modern political entity known as Spain only emerged after 1821, because before that the Castillian kings preferred to extend their domain across Northern Africa.
Though even in 1399 England had a formidable navy, it was not uncommon for smaller nations, upon successfully landing in their enemy's soil, to seize coastal provinces there.
The Russian principalities offered no great resistance to the Golden Horde, even under the leadership of the Muscowite princes.
Historical data concerning the rivalry between the Teutonic Order and their Prussian subjects is greatly exaggerated. Once the Reformation began, the Teutonic Order excitedly became the Kingdom of Prussia.
Despite there being numerous examples of it from antiquity, nations were unable to apply blockades on their enemies until they gained a certain "tech level".
The Reconquista was completed in 1400, not 1492. And then the Iberians took revenge by crossing the Mediterranean.
Despite the modern conception of Austria basically being Habsburg land in the fifteenth century, it was not uncommon for other familes to take control. The same often occurred within the Ottoman Empire, strangely without ever changing the name of the dynastically named state.
The term "balkanize" actually evolved from the word "francinize", because of numerous historical attempts to split France into many smaller states.