You do not own a country because you have grown up there and feel it better than the pockets of your pants. A nation is a linguistic construction. Like all languages, it is dynamic. It becomes and changes by being used. When people move into an area, it changes. That's how it should be. They have the right to move there, and nobody has the right to stop them. If you do not agree with this, you are a nationalist. You believe that countries, states, are something that exists in itself, regardless of the factual situation here and now. It doesn’t. This misconception is not necessarily malicious, you want to preserve something you think was there, or establish something you mean should be. But it does have harmful consequences for others here and now. The motive behind such a desire is self-interest, even if some may insist it is not.
For an internationalist, no borders exist, only places. Even if the physical location of a nation's border may exist, it has no practical meaning. Nobody owns a country and has any right to keep people out or hold them inside. That would be suppressing the ever-changing lingual condition of a state. As such, it is fluid and boundless whether we like it or not. Humans have a physical existence and a linguistic. The body has physical boundaries, but the mind or the self is continuously changing by being used. It is the same for nations. Not letting bodies wander is denying their changing inner self, and not letting countries change by these wandering bodies is denying that countries don't exist outside people's minds and thoughts. That they are made of the ephemeral material of language, just like us.