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|Jargon, buzzwords, slogans|
Fifth column is a term coined during the Spanish Civil War (1936-39) to designate a group within a population who are working to overthrow or disrupt the existing system - though the activity has been in existence for much longer. It is sometimes attributed to Nationalist General Emilio Mola, though the origins of the term are disputed.
In some contexts the term is used against groups who are exercising cultural and other affinities with groups outside the state but who are not actually attempting to overthrow the regime. Many xenophobic conspiracy theories center around some racial, ethnic, or religious group working to undermine glorious civilization.
In modern usage it is often use as a pejorative to refer to politicians and public figures who align themselves with foreign interests either discreetly or openly. Examples include British sometime-politician/blowhard Nigel Farage, who contributes extensively to Russian propaganda channels like Fox News and Russia Today. Alex Jones, Fox News and single-term US President Donald Trump have also been referred to as Fifth Columns.
There may be overlap between alleged fifth columnists and useful idiots.