Europe manage to handle those things just fine and local politics is very decoupled from EU politics. Why wouldn't states be allowed to close borders under emergencies?
Because a state is not a country. It doesn't have a military, border patrol, national guard, etc. That is to say, it doesn't have the manpower. And it could - practically speaking - never raise the money to do so (states have enough trouble paying their teachers, sanitation workers, paving roads, etc).
They have trouble paying for everything that’s on their wish list but that’s true of individuals and the federal government as well. A state COULD have those things, especially if their taxpayers gave up less in federal taxes since the federal government would have fewer responsibilities. Not sure how this changes things.
But if a state has sufficient personnel to handle an emergency (say a tornado strike on a town), they have too much personnel the rest of the time. Whereas, with a governmental entity, they can go from emergency to emergency, keeping wasted resources to a minimum.
The governmental agency can also shift resources from one state to another without having to wait for the resolution of aid politics between the individual states (not to mention the states the aid would be transported through).
Of course, there are significant inefficiencies that exist in those entities in reality, but what would realistically prevent those same inefficiencies from existing in a state-run system as well?
