Russia’s invasion of Ukraine has brought death, destruction and debate over historical analogies. Is this the summer of 1914, with great powers stumbling into a horrific global conflict? Or is it the Nazi-Soviet invasion of Poland in 1939? What about Moscow’s 1939-40 Winter War against Finland? Will Vladimir Putin’s gambit end like the Soviet Union’s 1979-89 misadventure in Afghanistan? Matt Pottinger has been thinking of another conflict. Mr. Putin’s attempted conquest, and his burgeoning partnership with China’s Xi Jinping, reminds Mr. Pottinger of the Korean War. “In 1950, Stalin and Mao and Kim Il Sung badly miscalculated how easy the...