XDocument.Descendants not returning descendants

You're not including the namespace, which is "http://www.lge.com/ddc", defaulted from the parent element:

XNamespace ns = "http://www.lge.com/ddc";
foreach (XElement element in xdoc.Descendants(ns + "nationalList"))
{
    ...
}

You have to use the namespace:

// do _not_ use   var ns = ... here.
XNameSpace ns = "http://www.lge.com/ddc";

foreach (XElement element in xdoc.Descendants(ns + "nationalList")
{
      MessageBox.Show(element.ToString());
}