$kml = new DomDocument();
$population = [];
$descr_tag = $kml->getElementsByTagName("description");
foreach($descr_tag as $d) {
    $pop = simplexml_load_string("<base>".$d->nodeValue."</base>");
    $population[] = (string)$pop->xpath("//li[strong/span[text()='Population']]")[0]->span;
}