This has been a concern in the prepper, formerly known as survivalist, community since its inception. Regardless of what author may have first written about it, the worry had wide currency long before it was written down. Thing is, the situation being cited as 'Golden Horde' isn't exactly what the concern is. In the present case, those refugees are fleeing Third-World shitholes to the wealthy URBANIZED areas of Europe, except to the extent they are corralled and kept in the countryside by force. The concern in the domestic prepper/survivalist community is the collapse of the technologically-highly-dependent DOMESTIC urban areas, with the outlying countryside being flooded by starving and rapacious masses of plunderers from the urban zones.