Ever since Vladimir Putin sent Russian tanks rolling into Ukraine in early 2022, assumptions about the possibility of war in the 21st Century have been turned on their heads. A long absence of conflict in Europe gave way to a bloody and sustained ground war. Russia has even warned it might unleash nuclear missiles. China, rattling its own saber in Asia, looms large in the background – just as it did in the ‘50s, ‘60s, and ‘70s. Nukes are the new normal. Hal Brands is a foreign policy professor at Johns Hopkins University, co-author of "Danger Zone: The Coming Conflict with China," a member of the State Department's Foreign Affairs Policy Board, and a Bloomberg Opinion columnist.