You can't fight what you don't know. You can't aim at something you don't see.
Just this morning, someone had shared a screenshot with me of a lady cheering about how nice it was that they as nationalists had international allies. The sharer's comment was how the lady wasn't using words correctly.
The sharer was an idiot.
He was conflating "international" with "internationalism", and thus equating it with "globalism". Any attempt at pointing out how he himself was conflating words was just "being autistic".
Definitions matter. There's a reason why liars actively attempt to stretch words past their definitions into an unrecognizable shape, because it allows them to quickly shift away from any lie they've told. "Now see, when I said ABC I really meant XYZ, so you can't really get so mad at me."
Clearly defining goals means you can actually, factually achieve them. Vague goals remain constantly out of reach no matter how far you progress, while clear and defined coals are within possibility. It may take a journey of a thousand miles but you can reach it eventually.
Defining who your enemies are allows you to defeat them. You don't spend time faffing about with whether certain person is really actually on your side or not, nor do you spend time and energy attacking people who are not actively working against you. Having clearly defined enemies is an aspect of the Geneva Conventions for a reason, and it's why guerrilla tactics are so frustrating because then it becomes almost impossible to define who's an enemy without including the entire population, and thus genocide.
Knowing the definitions of your ideology and of competing ideologies remains just as equally important, as not only do you have a clear goal to progress towards, knowing competing ideologies gives you a guideline on how not to slip into their concepts. Take the Conservatives in America. They have no actual guidelines, no core fundamentals, and it shows. The entirety of their accomplishments has been telling the Liberals, "Yes, but just not so fast". Exactly nothing has been conserved because they have no ideology other than "Well I liked things 20 years ago, but I can compromise".
If you know yourself and know your enemy, you will win 100% of your battles. Definitions. Matter.
So to define what the sharer got wrong, Globalism is the effort to make every nation the same. No borders, no restrictions on travel. They believe that all nations can profit together, all the time. And the reason why they do this, the end goal, is for one governmental entity to control as much as possible. Idealistically, this means one government that controls the world. Somehow this huge entity will put the entire world's resources to good use and do cool stuff like colonize Mars, or make all wars redundant, and never ever be corrupt and tyrannical.
Nationalism, amusingly enough, is only particularly defined in dictionary.com as being either patriotic feelings, or when you try to hold your country as being more important than other countries. Realistically, to understand nationalism is to understand what a nation is, and why it's different from a state. There's a reason why "nation-state" is a concept and not just a redundancy after all.
A nation is a group of genetically-related people. Always has been. The Cherokee Nation IS the Cherokee tribe. From small to large, it goes from you, your family, your tribe/nation. If you're genetically related, you have a large group of people that look like you for the most part, and act like you for the most part. That's powerful for building an identity, and an identity is crucial for mental stability.
The state is simply the government in charge of an area. When Rome had occupied Israel around Christ's time, they were the State. They definitely weren't genetically related to the Israelites. Empires are made up of many different nations of people, but the empire exerts power over them to bind them together as long as possible. That empire is the state. Thus, the nation-state is where a nation governs itself, and not others. Easy enough to understand.
Nationalism thus, in contrast to globalism, understands that not all nations can profit together all the time, and if you have to make a choice whether it's the other group or your group, your group comes first. Because if you don't place your group first, other groups certainly won't. It's hard to be non-identitarian in a world full of identitarians, after all -- you eventually wind up dying out.
Nationalism thus, in contrast to globalism, believes that one world government will never work, and every nation needs to govern themselves. No one will know their own nation as well as their own nation.
Germany for the Germans, France for the French. America, for the Americans. You know Americans, right? That genetic group of people who don't feel that incessant urge to hyphenate their ethnicity before the word "American"?