Final answer:
Charlemagne's conquests unified Europe under the Holy Roman Empire, which later fragmented but influenced future nation-state formation.
Step-by-step explanation:
The effect of Charlemagne's conquests on Europe was significant in that Europe was brought together as a single empire under his rule. Charlemagne waged wars to expand his territory and influence, resulting in the formation of the Holy Roman Empire, which was a vast state nominally controlled by a single emperor. This unity under Charlemagne's Empire did not last long after his death as the region eventually fragmented into separate kingdoms and states. However, his conquests laid the foundation for future developments in European nation-state formation.