What Makes People Proud of Their Country? (pewresearch.org)

Something that has helped them grow as a person or in profession. Or atleast something is a part of that nostalgic portion of their memories.

Probably if/when the country does things that makes the individual feel bigger or confirmed in the approach. So, if the person is altruistic, a country doing altruistic things makes them feel good and they're more fond of their country. However, if the person is an asshole, a country doing asshole things, etc.

People are proud of groups that do what they want, or let them do what they want. Good or bad.

A country is a fence around a piece of land. Odd in a way that people should feel anything about it.