South Korea's propaganda broadcasts: how do they work?

As the world mulls its response to North Korea's claims to have tested a hydrogen bomb, South Korea has stepped into action by resuming its propaganda broadcasts across the border. It may seem like a relatively restrained reaction to what the South's President Park Geun-hye called the "grave provocation" of the North, but the broadcasts have been a key bone of contention between the two Koreas.

How do the broadcasts work?

Propaganda programmes are blasted across the border using loudspeakers, targeting North Korean troops stationed in the Korean Demilitarised Zone (DMZ). While it is impossible to clearly measure its effects, the reaction of the North Korean regime suggests it fears their impact. In the past, North Korea has threatened to use force to silence the speakers and frequently blasts out its own propaganda in an attempt to drown out the broadcasts, The Guardian reports.

When did they start?

Radio has been used as a tool of psychological warfare since the Korean War in the 1950s, but in the 1990s, the South developed a more subtle approach. Taking a conversational tone, the broadcasts try to win over North Korean listeners with appealing portraits of life in the South and the benefits of reunification.

The South agreed to cease transmissions in 2004, but renewed them six years later, when relations deteriorated. Last year, they stopped them once again in an attempt to defuse mounting tensions after an incident in which two South Korean soldiers were injured by a landmine while on border patrol.

What do they say?

Main programme The Voice of Freedom sings the praises of democracy and life in the outside world as well as reporting news censored by Pyongyang's state media. Defectors from the North frequently speak on the air to report their experiences of freedom.

Aware that they are dealing with people raised in isolation from the outside world, broadcasters use a variety of tactics to win the trust of North Korean soldiers. One popular method is to put out accurate weather forecasts – something the technologically lacking North cannot do – to convince the soldiers that South Korea's information can be believed, the Korea Times reports.

Surprisingly, the most popular element of the broadcasts doesn't appear to be news from the outside world, but pop songs. The bubblegum sounds of South Korea's K-pop are an underground sensation in the North, defectors report, and are smuggled into the country on memory sticks and hard drives.