Download at http://www.cssscript.com/generic-country-state-dropdown-list-countries-js/
Create public/js directory and put all the .js file inside.
Create public/css directory and put all the .css file inside.
Add to the master blade head tags
<script type="text/javascript" src="{{ asset('js/countries.js') }}"></script>
Add to the bottom of master body tags area
<script language="javascript"> populateCountries("country", "state"); // first parameter is id of country drop-down and second parameter is id of state drop-down </script>