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In a major concession, Vice President Mike Pence has announced the Trump administration is willing to talk to North Korea without preconditions. Previously, the administration insisted that before negotiations could begin, the North had to agree to honor a previous commitment to not maintain an arsenal of nuclear weapons.

At the same time, Pence said South Korean President Moon Jae-in had pledged to continue the pressure campaign against the North Koreans until, in Pence’s words, they “are actually doing something that the alliance believes represents a meaningful step toward denuclearization.”

Pence revealed his exchange of promises with Moon to Washington Post columnist Josh Rogin aboard Air Force Two on the way back from South Korea. Rogin’s column was posted Sunday.

The North is unlikely to engage in substantive negotiations with Washington in the next few months, so Pence’s promise to talk may not mean much as a practical matter. But he did get a valuable pledge from Moon.

And there is another benefit from the exchange of promises. Pence and Moon avoided a split between their countries, which have been bound by a formal seven-decade-old alliance. They came up with a “real fix” as the Post aptly put it.

American policymakers worry about a breakdown in relations with South Korea, despite saying their alliance was “forged in blood.” And there is a real cause for the concern.

While the United States insists on the “denuclearization” of North Korea, Moon Jae-in’s apparent objective is unification of South Korea with North Korea. The American and South Korean goals, as a practical matter, clash.

Moon acts as if he believes that if South Korea unconditionally provides aid and assistance to Pyongyang for long enough, the North will eventually come around. That generous concept is at the heart of the Peace and Prosperity Policy of President Roh Moo-hyun, who governed the South from 2003 to 2008. Moon was Roh’s chief of staff.

The providing of assistance to the North fundamentally undermines the “maximum pressure” approach of the Trump administration, a plan to make sure North Korean dictator Kim Jong Un does not have money for launching missiles, detonating nuclear bombs and engaging in “gift politics” – the giving of luxury items to senior regime elements to buy loyalty.

And anecdotal evidence, stretching back months, suggests that President Trump’s policies are beginning to bite. North Korean officials are reportedly searching farm homes to take “every last grain of food inside.” Soldiers are getting months-long leave so they can hunt for sustenance. Due to the accelerated pace of missile and nuclear tests, Kim’s Office No. 39 slush fund is running low, according to Chinese sources.

Pence last week suggested Washington is going to clamp down even harder on Pyongyang. “I’m announcing today that the United States of America will soon unveil the toughest and most aggressive round of economic sanctions on North Korea ever,” he said while in Tokyo, before departing for Seoul. “We will continue to isolate North Korea until it abandons its nuclear and ballistic missile program once and for all.”

No wonder Kim launched an Olympics “charm offensive” and invited Moon to Pyongyang for what would be the third inter-Korean summit. He undoubtedly remembers that his father, Kim Jong Il, extracted an estimated $500 million in cash, under the table, from then-South Korean President Kim Dae Jung for agreeing to the historic first summit in 2000.

Will Moon do the same thing? He may not transfer money illicitly to Kim Jong Un, but he nonetheless hopes to support the other Korea in tangible ways. Moon’s administration, for instance, has floated various proposals, like reopening the Kaesong Industrial Complex. About 125 South Korean manufacturers operated in the complex in North Korea with Seoul’s blessing until the zone was shuttered in February 2016 by Moon’s predecessor, Park Geun-hye.

So despite his sweeping promise to Pence, do not expect Moon, on his own, to abandon the North.

Yet Moon, 65, does not have a free hand. His brand of Korean nationalism, which has widespread appeal in his left-leaning generation, is becoming unpopular at home, especially among the young.

South Korea’s president has seen his high approval ratings drop precipitously – 10 percentage points in two weeks in January, for instance – as he announced plans, among other things, to include North Koreans on the women’s ice hockey team.

Younger South Koreans generally see their society as separate from the North, not, as Moon envisions it, as one portion of a temporarily divided Korea.

And younger South Koreans have a point. The destitute, horrific North Korea shows up last in most metrics. South Korea is almost always near the top.

For instance, the South in 2016 produced $1.34 trillion of gross domestic product. North Korea managed just $28.5 billion. South Korea’s per capita GDP that year was more than 20 times larger than that of the North. The North’s per capita income in 2016 was 4.5 percent of the South’s.

But it is not just a question of economics as the Koreas have developed along starkly different lines. The customs and culture of the democratic South are almost unrecognizable from those of the totalitarian North.

Lee Jung-hoon, 30, told the French news service AFP that the North Koreans who had come down for the PyeongChang Winter Olympics “look like Koreans from a long time ago.”

Even the language has diverged so that there are now two distinct accents, and usage is no longer the same. About a third of common words in the two Koreas are different. As a result, the women on the unified ice hockey team, the first Olympic team fielded from both Koreas, had trouble understanding each other.

Those who have escaped the North and found their way to the South almost always have great difficulty adjusting from a totalitarian society to a free one. Some never are able to make the transition and, incredibly, return to the North.

This gulf between the two Koreas means the Trump administration has allies in South Korean society: those who do not want to see unification with a land they consider strange. And that means Washington, with its messaging, should be targeting the people of South Korea so that they will prevent their president from shoveling cash to Kim Jong Un and undermine international efforts to get Kim to abandon his nuclear weapons.