$(document).ready(function() {
  $("#country").change(function() {
    var new_state_link_href = $('#new_state_link a').attr('href');
    var selected_country_id = $('#country option:selected').attr('value');
    var new_link = new_state_link_href.replace(/countries\/(\d+)/, 'countries/'+selected_country_id);
    $('#new_state_link a').attr('href', new_link);
  });
});