Sovereign nation states are

Sovereign nation-states are formed on the idea of cultural unity.

Explanation:

When there is a single culture that the majority of the nation's people identify themselves with, the nation can be called a nation-state. In such countries, the majority population shares a common culture and believes in the idea of unity based on the widely followed culture. Because these people follow a common culture, their way of living, dressing, eating is all the same.