Build series of forts on our southern border and use these troops to sure it.
Well, don’t forget John Kerry’s wonderful declaration of the Monroe Doctrine being “over”. If the EU does become a military superpower, they’ve already got eyes on Central and South America, initially via Mercosur (following the EU pattern). Red China has been making very similar inroads there themselves. Both have been aiding the invasion of illegals across the border you’re referring to. We’ve never had to fight such a war so close to our soil; we’ve always gone abroad.