I have a form with 3 fields. Country, state and users

I am trying to do the following. when United states is selected as a country, the state field will show. The problem is that when i use the tab key on the keyboard, it is skipping the state field and its going on the users field. So i tried using the focus property so when i select United states, the state will show + selected, but I had no luck.. Below please find the code I am using
$(document).ready(function () {
$("#cmbCountries").change(function () {
$("#cmbCountries option:selected").each(function () {
if ($(this).text() == "United States") {
$("#cmbstate").show();
$("#cmbstate").focus();
}
else {
$("#cmbstate").hide();
}
});
}).change(); });
Any help please?
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