“Many artworks have sparked ideas, shaped sensibilities. The list of mind-changers in our history is a long, familiar one, from Machiavelli’s The Prince and Monet’s Impression: Sunrise to Simone de Beauvoir’s The Second Sex. But to have a direct, political effect – provoke a war, shape a law, inspire a cause – is much rarer.” Here are six works of art that had immediate impact on their times…