Sovereign nation states are

Answer 1

The most common political unit.

Answer 2

The most common political unit.

Answer 3

the most common political unit

Answer 4

A sovereign nation-state is the concept that a country is unitary and independent.

Since the Peace of Westphalia, all states agreed to not interfere in each others' internal political processes - thus, the state was sovereign.

A Nation and a State are slightly different concepts but a nation-state is more like a state than a nation. A State is a (geo)political entity, a nation is a cultural, racial, ethnic group of people, usually linguistically linked.

If we look at International Relations theory, Realist doctrine claims that all countries are unitary (act as a single actor), rational, selfish and independent of the whims of International organisations and regimes.

However, the sovereignty of nation states is believed to have been beginning to be broken down in the past few years with IOs like the UN and EU claiming sovereignty over some aspects of the nation state and R2P doctrine 'interfering' with their internal matters.

Answer 5

The most common political unit.