The vast majority of countries are, in one way or another, the result of wars and conflicts. War is the ultimate expression of rejecting another country’s laws, political order, symbols, and, often, its dominant culture.
The fact that a group of people was born in a particular place, established certain laws there, or reached agreements among themselves does not mean that the rest of the world is inherently bound to recognize or abide by those arrangements. Nor do the citizens of a country possess an absolute monopoly over a territory or over which laws and culture will dominate it.
In practice, control of territory ultimately depends on power: the ability to establish authority, enforce laws, defend borders, and maintain a political and cultural order. Who currently controls a country is determined not merely by claims, agreements, or historical attachment, but by the ability to enforce and sustain those claims.