Private property is a civilized abstraction that alleviates the requirement to kill people who enter land you've claimed for your own, for as long as you can defend it.
A made-up requirement, in which the centralization of abundance is justified on the basis of scarcity. Even in the feudal period, aristocracy came with obligations, like common access to land for purposes of passage or forage. Basically, this is just an excuse for people to claim more than they are able to use in the present, by asserting the necessity of them being able to do so in the future.
It's how national borders work.
A distinct negative, as far as I am concerned. Passports only became a thing around World War 1. Artificial restrictions on movement by labor is a massive economic distortion that essentially treats labor as a captive resource by mutual agreement between states. Would-be economic migrants whose goal is to work are equated with marauding armies.
That's also the time progressivism was peaking, and nation-states started creating centralized government welfare systems and engaging in Marxist revolutions.
Get rid of welfare states, and you can get rid of borders. But you can't maintain a welfare state with generous welfare subsidies and have open borders.
WW1 happened right after Roosevelt and Wilson got done debating who was going to be the best person to centralize state power in the national government in the mold of the social progressives. And just after Wilson outsourced American monetary policy to a banking cartel, which opened the way to unlimited war and an unlimited welfare state.
It's how national borders work.