The Synarchist Fifth Column

A Fifth Column is a group of people who undermine a larger group, such as a nation or a besieged city, from within. The activities of a Fifth Column can be overt or clandestine. Forces gathered in secret can mobilize when coordination with an external attack requires and extend even to uniformed military operations as part of a coordinated campaign. They can be clandestine, involving acts of sabotage, disinformation, or espionage executed within defense lines by secret sympathizers with an external force.

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wikipedia.org
http://www.larouchepub.com/other/2006/3323_france_fifth_column.html