Here's my idea of why nationalism exists in the first place.
From birth, no matter what ancestry we have, we are being told to respect it, to value it and cherish it.
I'm sure that in 99% of the world at least some people died for their country. I'm sure many of them died for the right cause, not knowing any better.
Take this into perspective. What is a country? A large group of people controlled by a small group of people occupying a certain territory. How do you die for that? Sure, died for revenge, avenge, glory, freedom... of what?
We are being thought that national pride is important just so we could be there when our government needs us. That's how wars get started.
Out of that, conclude that there is no greater power than large groups of people devoted to the same goal.
The before mentioned small group of people that run the Land know that as a fact. The ones in charge of the social structure of our Lands keep separating us into small and big groups, depending on what we're to be used for.
You and I are nothing but manpower.
When introduced to many ideologies, religions, identities, hierarchies, norms, ideas, idols and leaders, people will eventually split amongst eachother and blindly follow what their 'leaders' and 'idols' tell them is true.
The people who own us know that we cannot come together and bring them down. That has happened in the past, revolutions were powerful enough to overthrow instituted governments.
Can you imagine that happening today? There are 76 genders, how do you put them in the same room and explain we are being fucked in the same way by the same people when they believe they are anteaters in sexual life or whatever?
Nationalism is segregation.
You cannot just go with "My land is to love, other lands are to hate".
I will never die for a country. If it was worth dying for, we'd be much better off. We wouldn't have to be told to die for it, we would know it by heart.