JSFiddle - React, Tailwind, and code Playground

HTML

<select name="BillCountry" id="BillCountry">
<option value="">Select Country</option>
<option value="AS">American Samoa</option>
<option value="AQ">Antarctica</option>
<option value="CA">Canada</option>
<option value="UK">United Kingdon</option>
<option value="US" class="showme us-states">United States</option>
</select>


<select name="BillStates" id="BillStates">
</select>
<option value="" class="hideme">Select State</option>
<option value="AA" class="hideme">Armed Forces - Americas</option>
<option value="AE" class="hideme">Armed Forces - Europe</option>
<option value="AP" class="hideme">Armed Forces - Pacific</option>
<option value="AL" class="hideme">Alabama</option>
<option value="AK" class="hideme">Alaska</option>
<option value="AZ" class="hideme">Arizona</option>
<option value="" class="hideme">Select State</option>
<option value="AB" class="hideme">Alberta</option>

CSS

.hideme {
    display:none
}

.showme{
  display: inline-block;
}

JavaScript

$(document).ready(function() {  
   $("#BillCountry").change(function () {
       selOb=$(" :selected",this).prop("class")
       alert (selOb);
      $("#BillStates").addClass("showme")
   });
   
});