Illustration by David Simonds

LAST year, as Kenya slid into mayhem, the words that sputtered forth from crude transmitters were cryptic but, to those in the know, horrifying. “People of the milk”, a reference to the cattle-owning Kalenjin people, were urged to “take out the weeds in our midst”— in other words, the Kikuyus. Meanwhile Kikuyu broadcasters inveighed against the peril posed by “animals from the west”: this meant the rival Luo (from which Barack Obama originates) and Kalenjins.

In East Africa this use of radio to incite ethnic slaughter recalled an even darker episode: the Rwandan genocide of 1994, in which a station called Radio Mille Collines (Thousand Hills Radio) seemed to be directing the massacres. It not only poisoned the general atmosphere but urged on the killers, with phrases like “cutting the tall trees” and “killing the cockroaches”.

In an era of drones and spy satellites, it may seem odd that crude simple radio transmitters can still make huge mischief. But the scale and sophistication of broadcasting has mutated downwards as well as upwards. In the mid-20th century, totalitarian dictators found national radio stations were a handy way to foment hate and fear; and non-state actors (from communist guerrillas to churches) have been using radio for almost as long. In recent years the medium has been exploited in ever darker ways by petty warlords as well as by big-time tyrants.

Take the war zone on Pakistan's north-western frontier, where radio's sinister side has been on stark display. Scores of small FM transmitters—used to propagate extremist ideas and to terrorise local foes—have played a part in shoring up the Taliban's power. One notorious user of the air waves is Mullah Fazlullah, a Taliban leader in the Swat valley who is known as the “Mullah Radio” because of the threats he issues from an FM transmitter. After claims that he had been wounded, his voice was heard in mid-July for the first time in several months, albeit more subdued in tone than before.

Peacekeeping pundits agree that more must be done to pre-empt and counter the effects of “hate radio”. Nipping conflict in the bud by silencing dark propaganda would do a lot of good. If the problem were simply technical, it would presumably be soluble; an army bristling with space-age gadgetry must be capable of jamming a crude FM transmitter. But as anybody with experience of the problem confirms, neutralising nasty broadcasts is not so simple.

In Pakistan's war zones, a policy based purely on jamming, and confiscating kit, would upset local Pushtuns, for whom radio is a vital medium. Transmitters, often using batteries from cars or motorcycles, are easy to re-establish, says Mukhtar Khan, an analyst with the Jamestown Foundation, a think-tank in Washington, DC. He thinks the only antidote to hate radio is rival FM transmissions, run by locals who speak familiar dialects and cater to local interests, from farming to music.

A similar point is made by Eric Rosenbach, a veteran of American military intelligence (with knowledge of the Balkans and Iraq) who is now research director at Harvard University's Belfer Centre. “You can even further alienate a population if you take away their only source of information—but if you offer something new that's not obviously artificial, they may grab on to [it].”

American forces in Afghanistan already seem to be following that advice. They are making broadcasts of local interest and handing out wind-up radios.

In the world of journalism, meanwhile, some hard thinking is going on about how to stop abuse of the air waves. Radio Netherlands and Amsterdam University are refining a proposal for an early-warning system that would pick up hate-speech broadcasts, including cryptic ones, and at least mitigate their effects.

But Jan Hoek, who runs the global arm of Radio Netherlands, says he has grown cautious about lavish Western efforts to promote “good” media in places like Rwanda where radio was used for evil ends. It only works, he says, when locals are in the lead; otherwise the whole effort stops as soon as funds dry up. Despite these reservations, some fine courageous stations do now serve the region—such as Radio Okapi, broadcasting from Congo; two of its journalists have been killed.

For analysts of hate radio and its antidotes, the Balkans provide evidence of what works. The “ring around Serbia”, consisting of Serbian-language broadcasts from neighbouring states, which America helped establish, probably helped topple Slobodan Milosevic in 2000.

And in 1997, soon after arriving in Bosnia, NATO troops took swift action to seize transmitters and stop broadcasts by hard-line Serbs opposed to the Dayton peace deal. By contrast, during the bombing of Serbia in 1999, NATO lost support when it heavy-handedly hit the state broadcasting building in Belgrade, killing 16 staff. (A Serbian broadcasting boss was later jailed for not passing on NATO's warnings that the building was a target.)

Richard Holbrooke, the broker of the Dayton accord who is now America's envoy to Afghanistan and Pakistan, has named broadcasting as one area where lessons learned in one war zone must be transferred to others. In the Swat valley, he noted in March, “Fazlullah is going round every night broadcasting the names of people they're going to behead or have beheaded. Any of you who have a recent sense of history will know that that's exactly what happened with Radio Mille Collines in Rwanda.”