Vanilla JS snippet to generate a SELECT country list from an API.

select-countries.html

<select id="country" name="country">
    <option/>
</select>
<script>
    (async () => {
        const response = await fetch('https://restcountries.eu/rest/v2/all?fields=alpha2Code;name');
        const countries = await response.json();
        const select = document.getElementById('country');
        for (const country of countries) {
            const option = document.createElement('option');
            option.value = country.alpha2Code;
            option.innerText = country.name;
            select.appendChild(option);
        }
    })();
</script>