When dealing with various drop down list of options, with one acting as a filter to another and the last one being the desired option per se, it is more advisable to treat all drop downs as obligatory or just the final one used?
Let me set an example:
Country: [ select a country ⌄ ] State: [ select a state ⌄ ] City: [ select a city ⌄ ]
At first only the country drop down is loaded. As the user selects the country the state one got loaded. Finally, when the user selects a state, the city one is loaded.
Like: United States → Illinois → Chicago.
In the end what is really needed by the form is that the user is located at Chicago city.
If the user attempts to submit without selecting a state or a country, should it be warned that they are obligatory or just that the city it is (since the two first act as mere filters)?