"I love my country" or "I'd die for my country." People say that about their nation.
What is a nation?
The planet is artificially divided into countries. Artificial boundaries move over the centuries.
In earlier times people were more attached to their cave, village knowing little beyond. People were attached emotionally to the land that provided them food.
Rulers headed conglomerates of these smaller parcels. They tried to take ownership of other conglomerates, usually through wars, calling on the people to risk their lives.
Commonalities existed: language, habits, shared believes through religion, through festivals, through survival, through tragedies, through oral and written stories of the past, through dreams of the future.
In more advanced societies there was art, literature, music, architecture to celebrate and create pride. Stories convinced people they belonged to something bigger than themselves and greater than the conglomerate next door or across the sea. Differences in how one worshiped was always handy to convince people to fight for their nation. Gods beat land and wealth as a cause.
Leaders could be called chief, king, president, minister, general, oligarch. Some were good for the people: others were destructive. They made/make rules bringing order to the society which they oversee, but those rules control the mobs and help those leaders keep power.
Ever since one group of cavemen attacked another group with clubs and rocks in hopes of taking over a better cave, people have gone to war. The number of deaths mount. Lives of the warriors are cut short. Their heroism, their patriotism is lauded by the survivors, but in the long term or even the short term, they are forgotten.
The artificial borders shift, the reasons for the war melt into history. The actions of puny people fired with a sense of nationality and patriotism fall into nothingness.
And through the centuries for millions of years, the Earth keeps turning oblivious to those artificial constructs called nations.