Country, State, and City dropdown fields on user registration form

I am new to Drupal.

I have country,state and city field on user registartion form. If user selects country as 'United States' the State dropdown should auto populate with states belongs to "United States' . Same case with country. This is very basic requirement and i am wondering drupal doesn't support it!

For this, I have check the option_trim module. Its allowing to configure only for node types i.e: Group , page , poll etc..

But how can I configure it for User registration form?

Or Is there any other module for this or someway I can create this.