What are the dangers of extreme forms of nationalism?

People may follow their nation without objecting to its action. regardless of the attrocities that may be commited

Intolerance towards others who think differently, a drive towards protectionism through the passage of extreme laws and the use of tools (such as further legislation or internal services) to enforce control in order to promote the idea of the state, the idea that the nation is infallible and the conviction that it can do no wrong (whether it is in waging war to expand its influence or imprisoning people who speak out against it, for example).
 
These ideas can often be fostered under extreme forms of nationalism, especially if they have control of a country. One only has to look at what happened in Nazi Germany as a prime example.

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The answer is c socialist