Etymology of popular.

The Latin word for army is "populus" coming from the verb "populari", meaning "to plunder". When the army got to vote on political matters under Servius Tullius the word for army "came to designate the body politic" ('Ancient Rome', Christopher Mackay).

Hence the modern words 'population', 'popularity', etc are derivatives of plunder. So when the army goes into foreign countries to secure resources in the name of the people and supported by popular opinion, the etymological roots of popularism should become obvious.