Sure. But you still could draw some reasonable borders in most of the cases. Even the situation with USA vs. Native Americans and England vs. British Celts, that's conquest and they are different nations.
England and France shared core territory through the 1400s.
Rome constituted the core territory of the majority of Europe for a millenia.
Persia, Arabia, Rome, Byzantium and the Ottomans constituted the core territories of the Middle East.
The Mongol Empire constituted the core territories of China, Russia, Poland, the Middle East and Korea.
China constituted the core territory of Korea.
Japan constituted the core territory of Korea.
The Spanish Empire constituted the core territory of the Azetcs, the Maya and the Inca.
England, France and Spain each constituted the territory of what is now the United States and most of Africa and Asia to boot.
Vikings from both Denmark and Sweden have constituted each other's core territory, as well as that of England (in the Danish case).
Conquest or no conquest, there is significant overlap. Even without conquest, one can't draw reasonable borders around the fact that the Ottomans and Byzantium held (with a few territorial exceptions on the periphery of either power) the same territory.
If that overlap is taken out, then what are we left with? Certainly not England, Spain or France. Or anybody who was once owned by Rome, Byzantium, or China. Or Japan. Or the Mongols. Even the Indians would get the noose here, since their core territory has hosted the French, English, Portuguese, Arabs and Greeks.
.
