"State" requires "Country"
In the billing and shipping settings, if you deselect Country as shown/required, there's no setting that allows the State field to populate and no warning, so the cart just won't have the State field populated. It becomes an empty Dropdown with no mention as to why.
Ideally, just like with Shipping Zones, Country should be allowed to be predetermined if it's allowed for us to leave it off, otherwise it breaks the whole cart and people can't checkout.
In the current implementation, both the Country and State fields are required for the State dropdown to work correctly. The available states are loaded based on the selected country, so disabling Country while leaving State enabled results in an empty State dropdown.