North Korean leader Kim Jong Un, left, and South Korean President Moon Jae-in shake hands after their meeting in Panmunjom. (Korea Summit Press/Pool/EPA-EFE/Shutterstock)

South Korea’s Moon Jae-in and North Korea’s Kim Jong Un have startled the world by issuing their Panmunjom Declaration for Peace, Prosperity and Unification of the Korean Peninsula, including a plan to at long last go beyond the 1953 armistice and formally end the Korean War.

But while the declaration mentions “unification,” that doesn’t make the prospect imminent. For context, let’s explore the experience of another divided nation that came together unexpectedly: Germany, where East and West Germany united as the communist bloc crumbled with the Cold War’s end.

In 1989, East Germany lost its biggest backer. That has not happened to North Korea.

As communist regimes began to crumble throughout Eastern Europe in 1989, East German citizens in droves sought to leave for the West. They started by visiting neighboring Hungary, a Warsaw Pact member to which they could travel freely, in hopes of making their way to Austria and freedom. In September, when Hungary opened the border with Austria, East Germans began leaving for the West at a rapid pace.

Soviet leader Mikhail Gorbachev decided not to use military force to prop up the crumbling Eastern European regimes that had been part of the Soviet bloc. As Gorbachev’s spokesman quipped at the time, Moscow was no longer guided by the Brezhnev Doctrine that led the Soviets to intervene in Czechoslovakia in 1968, but was following the Sinatra Doctrine: Every country could do it their way.

With no help from Moscow, East Germany was increasingly helpless. When the East German government itself opened the border to West Berlin in November, thanks to accidental remarks by an East German Communist Party spokesman, it faced a rapidly deteriorating political situation.

Like the former East Germany, North Korea has been preventing defections — or escapes — through force. For years, the world has known that North Koreans have been suffering famine and starvation. In his meeting with Moon on April 26, Kim himself commented that he felt “embarrassed about the poor transit infrastructure” in his own country. Sanctions have surely hurt the North Korean economy.

But while standing in South Korea, Kim did not act like someone who faced an immediate crisis. Unlike the East Germans, he has both nuclear weapons and a patron, China, that does not appear to be abandoning him. He knows that China will not stand by and let North Korea be absorbed into the South on the latter’s terms.

The United States was committed to seeing a united Germany within NATO. It is hard to tell whether it is as committed to the alliance with South Korea today.

The United States was the major backer of West Germany — and eager to help West German Chancellor Helmut Kohl ensure that a unified Germany remained firmly in NATO. George H.W. Bush was president at the time, and as historian Hal Brands has recently written, was committed to a strategy of primacy. The United States sought not only to remain the world’s superpower with no peer competitor, but also to dominate every region of the globe, with no competing regional powers.

As the Soviet bloc unraveled in 1989, Bush had one goal firmly at the forefront: ensuring that the collapse of communist regimes did not lead Europeans to doubt that they still needed NATO. After all, NATO was the vehicle by which the United States dominated European security affairs. Without NATO, the United States might become a bystander in Europe.

For someone of Bush’s generation, the two world wars had taught a clear lesson. After 1918, the United States withdrew from Europe, a move that ended in disaster. After 1945, the United States remained deeply engaged with Europe, a policy that was a huge success.

Thus, if Germany unified, Bush wanted the country fully in NATO. This required extraordinarily deft diplomacy. British Prime Minister Margaret Thatcher and French President François Mitterrand opposed unification, because they feared a more powerful Germany. Gorbachev not only opposed unification, but he opposed East Germany’s becoming part of NATO. After all, East Germany had been the Soviet Union’s big prize after World War II, a prize that had cost tens of millions of Soviet lives. Domestically, Gorbachev was challenged over this issue. Even within West Germany, some political leaders were willing to forgo NATO membership (or, at least, bringing East German territory within NATO) to get unification. But Bush held firm on NATO membership and ensured that Kohl did so as well, enabling the United States to continue its leadership role in Europe.

The Russians were not particularly happy with the result, and their distaste for how German unification proceeded remains part of Russia’s grievance against the West today. But in 1989 the Soviet Union was weakening — unlike a rising China today.

Unlike West Germany then, South Korea today does not seem to have its superpower ally’s unwavering support. President Trump has vacillated about U.S. relations with its allies in Asia. Just last month, he threatened to withdraw the U.S. military from the Korean Peninsula if he could not get his way on issues such as trade. That will make the South Koreans less sure they can count on the United States during any negotiations than Kohl was in 1990.

But each country’s supporting great power has to be involved as negotiations move forward.

And yet the two Koreas’ respective great-power backers will have to be involved as things unfold. Moon and Kim announced that they are planning quadrilateral meetings among the two Koreas, the United States and China, all of which must be involved to bring a formal end to the Korean War.

Similarly, the two Germanys could not accomplish unification by themselves. Four countries had administrative rights in Germany after World War II: the United States, Britain, France and the U.S.S.R. All were included as part of the “2+4” unification negotiations to ensure that everyone eventually got on the same page.

The role China and the United States will play as the Korean situation unfolds is similarly critical.

In 1989-1990, events moved faster than anyone imagined possible, even Kohl and Bush. Few could have believed when the Berlin Wall fell on Nov. 9, 1989, that Germany would be unified less than a year later. Having seen Kim develop his nuclear program and stand as an equal to his South Korean counterpart, it is hard to imagine he would simply give up the game as the East Germans (and their Soviet ally) did in 1990.

And that is perhaps the last lesson. We understood unification in 1990 as East Germany being absorbed into the West. It is unlikely Kim (or Xi Jinping) will see unification in similar terms today.

James Goldgeier (@JimGoldgeier) is professor of international relations at American University and visiting senior fellow at the Council on Foreign Relations.