Historically, this led to the Scramble for Africa and ultimately, WWI - which itself led to WWII. But hey, I'm sure your concerns are all about writing great national anthems instead of punching down on those you see as other, huh
Again - THAT COUNTRY'S people. Therefore, it necessitates the creation of enemies - foreigners, aliens, outsiders that are beneath you because they are not a part of the country that you are.
Nationalism was born in the late 18th century when workers engaged in big, national economies for the first time, thanks to the Industrial Revolution. Philosophically, it is a social contract between the state and the people.