TOKYO -- When one talks of tensions on the Korean Peninsula, propaganda leaflets and loudspeakers have their own history with links to the present.
In the past, it was the South Korean military that jeopardized relations with North Korea by using them.
This time, it was a group of North Korean defectors in the South who launched leaflets criticizing the North's regime under Supreme Leader Kim Jong Un, triggering it to demolish the building housing the joint liaison office between the two Koreas.
The North is also threatening to deploy its military at the Kaesong Industrial Complex and the Mount Kumgang Tourism Complex, which both lie near the Demilitarized Zone between the two countries and once symbolized detente and hopes for peaceful coexistence.
Fighters for a Free North Korea, a defector group in South Korea, on May 31 released 20 large balloons over the border, each carrying 500,000 propaganda leaflets, 50 booklets, 2,000 one-dollar bills and 1,000 USB memory sticks.
The liberal daily Hankyoreh and other South Korean media reported that the leaflets were critical of the North's regime, including slurs against Kim. Booklets condemned the North's nuclear ambitions and urged people to rise against their regime. USB memory sticks contained footage of advanced South Korean society and a lawmaker who had defected from the North.
Defectors are treated like criminals in the North. Pyongyang is particularly sensitive to propaganda leaflets and broadcasts circulated by defectors and conservative activists.
Kim Yo Jong, the sister of Kim, earlier this month branded defectors "human scum" and "mongrel dogs" for flying the hot air balloons carrying anti-Pyongyang propaganda.
North and South Korea have previously clashed over propaganda leaflets, as well as loudspeaker broadcasts from the South.
In 2014, the two sides exchanged fire over propaganda balloons released by a South Korean conservative group near the DMZ. A few days before the incident, a North Korean security boat had crossed the Northern Limit Line in the Yellow Sea, which demarcates maritime territory between the countries, prompting the South to fire warning shots.
Observers pointed out at the time that the incident was linked to health concerns about Kim.
Some believe the North, at the time, was taking stronger measures against the South to increase the morale of its soldiers and people, after footage of Kim limping was broadcast recently, speculation spread that he was ill following surgery, and there has been little up-to-date information about him.
In 2015, the South Korean military's large loudspeakers in the DMZ provoked a backlash from the North. Propaganda broadcasts, starting with "Dear fellow Koreans in the North," criticized the North's systems and poor human rights record. The broadcasts stressed the superiority of the South's liberal regime and highlighted the lavish lifestyle led by Kim and his wife. It was said that the broadcasts could be heard as far away as 10-20km.
The North demanded that the broadcasts stop, issuing a statement saying that it would put the DMZ on a "quasi-war" footing and would not hesitate to engage in an all-out war. It called for talks after "repeated provocations."
To broker the crisis, the two sides held high-level talks over 43 hours, and agreed on six items to de-escalate tensions. These included the North expressing regret over an incident in which two South Korean soldiers were badly injured in a mine explosion, which had prompted the South to launch the propaganda broadcasts. In return, the South agreed to discontinue the broadcasts.
"I believe that anti-North propaganda broadcasts by the South are a decisive factor that could threaten the stability of the Kim Jong Un regime," said a former South Korean military official, who headed North and South military talks in the 2000s, on the incident at the time. "In order to maintain the Kim Jong Un regime, it is extremely important for the North to keep external information away from the eyes of its soldiers and people."
"If soldiers and residents in the Demilitarized Zone are exposed to external information, Pyongyang's lies, aimed at justifying the Kim Jong Un regime's failures and powers, will come to light," he added. "The North strongly opposed and tried to stop the broadcasts as they could shake unity among its soldiers and people."
The North is particularly sensitive about personal attacks on Kim, to whom it refers as the "supreme dignity."
The South Korean military was targeting North Korean soldiers on the front line in its propaganda broadcasts, in the hope that when they return to urban areas like Pyongyang after ending their missions, the propaganda would spread among ordinary citizens via word-of-mouth and shake loyalty to the Kim regime.
During the 2014-2015 period when these broadcasts were common, Park Geun-hye, who regarded the Kim regime as an enemy, was South Korea's president. Through a tough stance and not giving an inch to the North, the conservative politician managed to extract concessions from Pyongyang.
South Korea is now led by the more progressive administration of President Moon Jae-in, which attaches importance to harmony between the two Koreas. After facing a strong protest from the North over the leaflets sent across the border, the Moon administration filed a criminal complaint against two defector groups, including the Fighters for a Free North Korea, on suspicion of violating the inter-Korean exchange and cooperation law.
Meanwhile, the North has not stopped its own provocations. There are growing concerns that Pyongyang might further accelerate its hard-line stance in the future, taking advantage of what it perceives as a weakness in the Moon administration.