How borders are drawn and enforced has far-reaching consequences, whether we live on either side of them or halfway across the world.

Last month South Korea and the US finalized plans for an anti-missile defense system to protect against potential attacks from North Korea. While news of that system and possible reactions to it grabbed headlines, a less-noticed deterrent has been rapidly mobilizing in recent years: Chinese tourists.

Nearly half of the 6.5 million tourists visiting South Korea in the first five months of this year came from China. That’s a steep climb from 675,000 for the same period of 2010. Beijing—Pyongyang’s only real ally and trading partner—may not look kindly on North Korean dictator Kim Jong-un threatening to turn Seoul into a on fried chicken and beer there.

The presence of nearly a million Chinese tourists in South Korea during any given month now joins the US military and guided ballistic missile systems on the list of deterrents against North Korea launching an attack, said Brian Moore, resident fellow at the Pacific Forum at the Center for Strategic and International Studies in Honolulu.

“An attack that results in Chinese deaths may increase the likelihood that Beijing permits, and perhaps joins, the US-South Korea counter-attack,” Moore said. “In the more recent conflicts that have resulted in deaths… they made sure that only South Koreans were targeted.” In 2010 for instance North Korean artillery shelled the border island of Yeonpyeong, killing four South Koreans.

To complicate matters, Beijing isn’t happy about the anti-missile system—Terminal High-Altitude Area Defense, or Thaad—being planned by South Korea and the US, and might retaliate in a number of ways on the economic front. How that will affect the number of Chinese visitors remains to be seen, but South Korea’s tourism industry is already worried. Hotel Lotte, the nation’s biggest operator of duty-free stores, told Bloomberg visitors from China accounted for 70% of sales at its duty-free stores in the first six months of the year.

Meanwhile, Chinese tourists are flocking not only to Seoul and other parts of South Korea, but also to the Demilitarized Zone (DMZ) that divides the north and south, which have formally remained at war since the 1950s. The area remains one of the most militarized places in the world, despite Kim’s seemingly erratic behavior and recent spate of missile tests. One tour company offering trips to the DMZ advertises it as “the safest battlefield in the world.”

The DMZ has long attracted tourists from around the world eager for a taste of war kitsch and excitement, and now Chinese tourists are increasingly among them. On a recent Saturday, hundreds of them boarded buses that drove along the Han River to the rural area surrounding the DMZ. Ron Han, a guide on one of the buses, pointed out the part in the river where the South Korean military picked up a Texas man who had attempted to swim to North Korea to meet Kim (he later succeeded by swimming across the Yalu River from China).

“I think he made a completely wrong decision,” Han told the passengers. “The best way and easiest way to defect is to take the tour. You can just jump over.”

The only items on the tour sourced from North Korea are old bottles of shoju liquor made with rice and ginseng, which the country supplied before military skirmishes in 2010 resulted in a severing of gift-shop relations.

“There’s no place to buy North Korean currency. It’s illegal,” Han told the tourists. “But I suggest the North Korea liquor. It’s quite worth it.”

Chinese tourists aren’t just visiting South Korea and the DMZ. Recently the Kim regime started allowing them to visit a limited section of North Korea for up to half a day without a passport. Thanks to a new round of international sanctions, the regime needs hard tourist cash more than ever. The tourists pay $52 to sign up for a tour that takes them from the port city of Dandong, the biggest Chinese city along the 880-mile border with North Korea, across the Yalu River to the North Korean city of Sinuiju. Besides being a major trading hub between the two countries, Sinuiju is also home to a Ferris wheel.

“The last thing Kim Jong-un would dare to do before going completely bonkers is to kill thousands of Chinese tourists at the DMZ and in Seoul,” said Bradley Martin, a longtime North Korea watcher and author. “China has matured to the point where it cannot write off the sacrifice of large numbers of its citizens. Many—including those who take DMZ tours—are monied people who can’t be wiped off the face of the Earth without repercussions.”

You can follow Ben on Twitter at @bjlefebvre.