The world’s most powerful nations will soon find out if they can prevail over one of the weakest. In a historic agreement reached last week, North Korea promised America, China, Russia, Japan, and South Korea that it will implement a two-step plan to dismantle its nuclear weapons program. In the first stage, lasting just 60 days, the militant state will shut down and seal its main reactor in Yongbyon, north of the capital of Pyongyang. International inspectors will monitor this activity. In the second, the North Koreans will disable all their nuclear facilities and disclose all nuclear programs.

What will the North Korean leader Kim Jong Il get in return? America and Japan will lift some sanctions and start the process of normalizing relations. But more important is the tangible benefit of obtaining heavy fuel oil from America and other nations. For the first step, Pyongyang will get 50,000 tons of it — or aid in an equivalent amount. For the second, there will be an additional 950,000 tons of oil or aid.

John Bolton, former U.S. ambassador to the United Nations, immediately blasted the agreement, saying it rewards North Korea “with massive shipments of heavy fuel oil.” The value of all the oil, however, is only about $250 million according to Christopher Hill, Washington’s chief negotiator with North Korea. So is Pyongyang willing to give up its nuke program for such a small amount? The value of the fuel oil, after all, is only one-sixteenth of Kim Jong Il’s estimated personal net worth.

It is unlikely that the North Korean supremo intends to surrender his weapons-producing facilities for any sum. North Korea has spent billions of dollars to run its bomb program for at least four decades. Kim Il Sung, the current leader’s father, got the Soviets and Chinese to transfer nuclear technology shortly after the end of the Korean War. In the middle of the 1960s, Moscow helped the North Koreans build the Yongbyon reactor. Then North Korea kicked its nuclear arms program into high gear, sometime in the late 1970s.

Although anything is possible in North Korea — the place gives new meaning to the word “bizarre” — it is improbable that a militant nation will ever surrender its most destructive weaponry. As Kim Kye Gwan, Pyongyang’s chief nuclear negotiator, said last December, “Do you believe we developed and sustained our nuclear weapons programs for so long just to give them up?”

Kim Jong Il’s nuke program makes him geopolitically relevant, ensures aid from foreign nations, and destabilizes archenemies South Korea and Japan It provides an “aura of invulnerability” and therefore ensures the survival of his one-man regime. The weapons program is the only success he can point to in more than a decade of misrule. Without his atomic bombs, he would be just another ignored leader of one more failing state. With them, he is a fearsome autocrat and the center of the world’s attention.

So why did Kim Jong Il agree to shut down his nuclear facilities? The most likely explanation is that he wants enough fuel oil to get through the rest of this winter and that he will renege in the spring. Indeed, Pyongyang now says that the deal, which everyone else thinks requires permanent disarmament, only contemplates a “temporary suspension.” Whatever his intentions, Washington needs a plan to make sure Kim honors this agreement, because he and his father have breached every other nuclear pact they ever signed.

The deal will work, but only if Beijing and Seoul stop funneling aid to Pyongyang. In the past few years, China has provided about 90% of the North’s oil, 80% of its consumer goods, and 45% of its food. Most of this appears to be provided on concessionary terms. South Korea, for its part, also has been a major aid contributor, especially of food and fertilizer. Assistance from China has fallen dramatically since Pyongyang’s missile tests last July, and South Korea suspended aid entirely. Therefore, it is no surprise that Kim Jong Il settled for such a small amount of oil last week. Yet if Kim now gets extra food, commodities, and oil from these two patrons in the weeks and months ahead — and Seoul has already indicated it will step up aid shipments — the pressure to carry through on the nuke deal will be off. Up to now, North Korea has been able to defy the international community because Beijing and Seoul have presented a united front in supporting Pyongyang. Therefore, Washington needs to use deft diplomacy to drive a wedge between those two countries. The presidential election in South Korea this December presents a golden opportunity to strip Seoul from the Beijing-Pyongyang axis. All indications point to a conservative win at the end of this year. If South Korea more closely aligns its policy with ours, China will be alone in its support of Pyongyang. Then, Washington can use leverage to force the Chinese to make the right choice between their future — cooperation with us — or its past — its alliance with North Korea.

So Washington, by leaning on the Chinese, can create the miracle of North Korean disarmament. It’s time for some good news from North Asia.

Mr. Chang is the author of “Nuclear Showdown: North Korea Takes On the World.”