JSFiddle - React, Tailwind, and code Playground

HTML

<fieldset id="billing">
    <select id="country-a">
        <option>Select a country</option>
        <option value="United States">United States</option>
        <option value="Ukraine">Ukraine</option>
    </select>
    <select id="state-a">
        <option>Select a state</option>
        <option>state one</option>
        <option>state two</option>
    </select>
    <input id="state-field-a" />
</fieldset>
<fieldset id="shipping">
    <select id="country-b">
        <option>Select a country</option>
        <option value="United States">United States</option>
        <option value="Ukraine">Ukraine</option>
    </select>
    <select id="state-b">
        <option>Select a state</option>
        <option>state one</option>
        <option>state two</option>
    </select>
    <input id="state-field-b" />
</fieldset>

JavaScript

var countrySelects = '#country-a, #country-b',
    stateSelects = '#state-a, #state-b',
    stateInputs = '#state-field-a, #state-field-b';    
    
$(stateInputs).hide();

$('fieldset').each(function () {
    var $fieldset = $(this);
    
    $(countrySelects, $fieldset).change(function () {
        var $countrySelect = $(this),
            $stateSelect = $(stateSelects, $fieldset),
            $stateInput = $(stateInputs, $fieldset);
        
        if ($countrySelect.val() === "United States" || $countrySelect.val() === "Canada" || $countrySelect.val() === "null") {
            $stateSelect.show();
            $stateInput.hide();
        } else {
            $stateSelect.hide();
            $stateInput.show();
        }
    })
});