In an age of social media and “spin”, propaganda permeates communication as much as ever, argue the show's curators. The lavish opening ceremony for the 2012 Olympic Games in London was a classic exercise in national branding, for example. Similarly, last month's ceremonial pomp for Margaret Thatcher’s funeral served to reinforce enduring symbols of British authority. The most re-tweeted tweet in history, “Four more years” (celebrating Barack Obama’s re-election as America's president), illustrates mass dissemination of a particular point of view.

STATE propaganda is easy to spot. From leaflets dropped behind enemy lines to other bald appeals to flag and country, government attempts to sway public opinion often seem laughably obvious—at least in hindsight. Yet quite a lot of national pride-mongering is a bit more subtle—and more effective, and perhaps more troubling—than we like to admit. This at least is the claim of “Propaganda: Power and Persuasion”, a provocative new exhibition at the British Library in London.

“When people think of propaganda, they often think it’s only done by the bad guys,” explains Ian Cooke, who co-curated the exhibition. In fact propaganda is “everyday and insidious”, produced everywhere and by everyone. By offering contemporary examples of this age-old practice, this show pushes visitors to reflect on their own susceptibility to manipulation.

The word “propaganda” first appeared in print in 1622. The Roman Catholic treatise urging “propagation” of the faith is displayed in the show's opening section. But the practice predates popes and Martin Luther, beginning with Greek coins imprinted with the guises of rulers. It was not until the early 20th century, however, that propaganda as we know it flourished. Rare historical objects from this period alone make this show essential viewing. These include Chairman Mao’s “Little Red Book”, Josef Goebbels’s cheap radios sold for Nazi broadcasts (known as “Volksempfänger”), posters of Hitler as a national saviour (“Ein Volk, Ein Reich, Ein Führer”), and “Mao Goes to Anyan” (pictured right)—the most reproduced image in history, printed 900m times. Building national loyalty is especially vital in wartime, when enemies must be demonised and loyal citizens alternately comforted, alarmed and exhorted to sacrifice. Such aims are plain in propaganda developed during the 2003 Iraq war.

One of the show's highlights is a mint-condition set of Norman Rockwell posters entitled “The Four Freedoms”, on loan from a London gallerist. Designed to persuade Americans to buy war bonds during the second world war, these 1943 posters raised $130m by depicting the national values of family, prayer and the nobility of the workingman. A similar note is struck by a 1942 scarf with a map pinpointing bomb strikes, printed with the slogan “London Can Take It” and part of Winston Churchill’s famous “We shall fight them on the beaches” speech.

Methods of fear-mongering and intimidation, like those of reassurance, do not change much over time, Mr Cooke says. On view are the renowned Iraq playing cards distributed by the American military, which bore photographs of most-wanted Iraqis and featured Saddam Hussein as the ace of spades. The purpose of the cards was two-fold, he says: first as an aid to capture, and second to demonstrate power and control, “to say ‘we know who you are’.” The show also includes a notorious example of false propaganda: a front page of London’s Daily Express with the headline “Saddam Can Strike in 45 Minutes”. Based on deceptive government statements, the scare tactic helped propel Britain to war in 2003.

It is the difficulty of separating truth from propaganda in the volume of today’s communications that worries the experts. The final piece in the show is an electronic wall that displays Twitter traffic from the London Olympics, Obama’s re-election, and the recent mass shooting at a school in Connecticut. “In a global, social-media world, do we know who these people are? They’re all talking,” reflects Jude England, the library’s head of social science. The tweets parade by, spiking and subsiding; at home, our Facebook feeds crawl with marketing pitches; book reviews on Amazon are penned by paid guns. Individuals, paid lobbyists, corporations, activists: “It’s not entirely clear who’s behind these things,” Ms England observes.