The shock of Russia’s invasion led Germany to discard six decades of military-averse policy rooted in its own wartime experience. Chancellor Olaf Scholz announced the Germans would ship Ukraine 1,000 shoulder-launched antitank rockets, 500 surface-to-air Stinger missiles and 2,700 Soviet-era shoulder-fired missiles — as well as embark on a mammoth, $110 billion rearming program at home.

It led the once-divided European Union to unite behind choking sanctions that will ban Russia’s central bank, which holds Mr. Putin’s war chest, from selling any assets to European banks. Brussels, long derided as an economic giant but a foreign-policy dwarf, pledged to spend $500 million on defensive weapons for Ukraine.

It led Mr. Biden to recast a presidency that had been focused on rebuilding America after the coronavirus pandemic and confronting China to one that is waging a twilight struggle against a Cold War rival on the plains of Eastern Europe.

It has reverberated not just in the councils of state, but also in corporate suites, cultural institutions and sports leagues — to say nothing of city streets from Mexico City to Madrid, where tens of thousands of demonstrators have waved the yellow-and-blue Ukrainian flag and chanted against Russia’s aggression.