Taken as a whole, countries are typical examples of places with a fairly clear set of customary beliefs, social forms, and material traits of a racial, religious, or social group.

Or simply stated, countries have a unique culture embraced by their populations.  This does give rise to stereotypes or unconscious bias but in the case of countries, there is always some root basis to the cultural interpretation.

For example, Canadian culture is often stereotypically defined as polite.  Not all Canadians exhibit excessive politeness or repeatedly apologize but on the whole, this is a national trait and arises from a natural observation of the populous as a whole.

How does this happen

Assuming you can except national cultural stereotypes exist and do have some basis in reality, the question becomes, how does this happen?

The most common methodology is for cultural behaviors to be enforced, largely through consequences.  From a young age, we are trained to conform to societal beliefs through the carrot (positive consequences) and the stick (negative consequences).

Some societies, I believe Japan is a good example of this, develop conformance to the expected behaviors collaboratively.   That is through example and individual interaction where the reason for the overarching beliefs is developed individually, not forced but absorbed.

While much harder to achieve, absorption of cultural values through self-learning rather than enforced training is much more effective and most importantly sustainable.

Left or Right (somewhere in the middle)

The downside, to both practices of forming a common culture, is the impact on the individual.   The balance between total individual freedom (anarchy) and a rigidly established society (authoritarian) is the sweet spot cultures should naturally try and attain.

When cultures grow organically they are more likely to be balanced.