See also Bénédicte Savoy's reference work (on Napoleon's plunder / booty resp. "Kunstraub" in Germany):

http://www.amazon.de/Kunstraub-Konfiszierungen-Deutschland-europaeischen-Kunstwerke/dp/3205784278/

I think, "art requisition" is somewhat flattering - I would reserve the term "requisition" for necessary army wants, like provisions or fourrage .

Best regards, Thomas