A cashiered Athenian general, Thucydides, famously explained the cause of the Peloponnesian War (431-404 B.C.): “War became inevitable with the growth of Athenian power and the fear this caused in Sparta.” This explains many wars. With North Korea, the Thucydides trap may be starting to shut.

North Korea has perhaps 20 nuclear devices and improving missile reach. Supreme Kid Kim Jong Un just proclaimed they’re getting ready to test an ICBM. In four years, some estimate, a nuclear-tipped North Korean missile could hit the U.S. A frightening logic kicks in: If war is inevitable, sooner would be better than later for us. Or — one theory of the Cold War — nukes are unusable, but mutual deterrence contributes to caution and stability, provided possessors are rational. Place your bets.

North Korea, convinced that only nukes protect it, won’t disarm. As Secretary Tillerson emphasized in Seoul, diplomacy was tried for years and our “strategic patience” is over; he did not exclude war. This policy is consistent since Truman and Eisenhower publicly pondered nukes during the Korean War; only Tillerson’s verbal openness jolted. It seems to not have occurred to Pyongyang that nukes may provoke rather than deter. North Korea does a lot of provoking, recently in launching missiles toward Japan, showing that U.S. bases there are vulnerable. 

Provoking North Korea into war is tempting. Pyongyang swears that the slightest U.S. incursion into its territorial waters will bring a rain of fire. So, without hiding it, intrude a little. Or just say you did. If North Korea does not respond, they will have been caught bluffing, a big mistake in international relations (that we too must guard against).

Probably North Korea is not ready to strike. Should we wait until they are? North Korean artillery can hit Seoul, but it would quickly be silenced and other military targets destroyed, especially nuclear facilities. Such a war need not go nuclear but easily might. No, I’m not looking for war; I’m hoping Washington can get China worried enough to step in.

Beijing, while scowling at Pyongyang, refuses serious pressure because, it says, that might collapse the regime. The assassination of the young dictator’s half brother with VX nerve agent enraged Beijing, who let him live in Macau (he liked to gamble) on a Chinese passport and stipend. Some speculate that Beijing was keeping him in reserve in case of upheaval in Pyongyang. (Malaysia’s reluctance to break diplomatic ties with North Korea over this murder showcases weakness.)

But China is still unwilling to lean on North Korea, it claims, because that might send millions of refugees across the Yalu River into Manchuria. Dubious. China has ample security forces to block that. A better explanation is that Beijing does not want U.S. forces (or U.S.-allied South Korea) on its border. The last time they approached the Yalu, in late 1950, China intervened massively. Actually, the People’s Liberation Army was already positioned to enter the war near that border before North Korea invaded South Korea in June.

But separation of forces could be provided for. Washington could affirm that no U.S. forces and only light South Korean forces will move north of the present demilitarized zone in the event the Pyongyang regime collapses. Or let China take over North Korea and run it as a Special Administrative Region, as it does Hong Kong and Macau.

I suspect Beijing wants to keep North Korea as a pit bull chained to the front gate as it prepares for a showdown in the South and East China seas. If South Korea and Japan have to worry about North Korean missiles, so much the better to keep them occupied and out of our seas. You cannot separate the North Korean nuclear issue from China’s hegemonic and territorial ambitions in the region. Interestingly — and sadly — Beijing has frozen its burgeoning relations with South Korea over the installation of a U.S. Terminal High Altitude Area Defense (THAAD). 

Defense Secretary Mattis just reaffirmed an “overwhelming” U.S. response to a North Korean attack. In deterrence theory, this should favor stability but does not preclude war by miscalculation, which nearly happened with the Berlin Wall in 1961 and Cuban missiles in 1962. The Korean War itself was a miscalculation that the U.S. would not intervene. Washington in early 1950 had no such plans, but the specter of a rapid expansion of Stalin’s power quickly decided Truman. Overnight, South Korea went from unimportant to vital.

New trouble could flare if President Trump threatens Xi Jinping in Florida next month with U.S. “secondary sanctions” on Chinese firms and banks that do business with North Korea. Both sides’ positions are firm: The U.S. will defend South Korea, and China will claim Taiwan and the China Seas, a difficult situation to preserve if Beijing lets its small ally make perilous decisions for it.