New Delhi, Jan. 26 -- Recently, Prime Minister Mark Carney of Canada delivered a talk on rupture to rapturous applause. At Davos, Carney's attention-getting point was about the end of the international "rules-based order" and its replacement by "might is right."

In his view, this rupture is real and irrevocable and demands both individual and collective action by "middle powers." Deservingly, he has been praised for his courage and clear-headed reading of realpolitik. Carney suggested that Thucydides's aphorism that "the strong do what they can and the weak suffer what they must" need not be considered inevitable in this new order.

Writing about 2,400 years ago, Thucydides, a historian and general in ancient Greece, offered profound ins...