Usually, a good strategy for improving the form is to minimize fields, merge them, and simplify the form. In the case of address input, the rules change. Combining address fields into a single input may not be a good idea.
If the field is optional, it doesn't need to be shown in the form. This is a very simple principle that always works. In many countries, the state or region does not matter when you enter an address. Therefore, it makes no sense to show an extra field.
It is always best to hide the state or region input if it does not matter in the user's chosen country. Or conversely, show the state field if you selected a country where it is relevant.