Every venue must be assigned a State. In some environments, if your account has no states at all, opening the Venues page shows the pop-up States Missing (Hey we notice you're trying to create a location, however to do this you first need to create a state) with a Create a state button, and the add/edit form redirects back to the list until a state exists. Create at least one state under Delivery Settings > States, then come back and click Add new.