“The logic of mutually assured destruction that defined the Cold War still works, to some degree: Russia’s arsenal makes any direct intervention in Ukraine riskier than any rational American leader could tolerate. In a sense, then, Russia’s nuclear weapons make it less likely that the conflict will kick off World War III.
But in another sense, Russia’s nuclear arsenal also helped create the conditions where Putin’s invasion could happen in the first place.”
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“Russia can be relatively confident that the United States and its allies won’t come to Ukraine’s defense directly, because such a clash carries the threat of nuclear war. This could make Putin more confident that his invasion could succeed.
Putin himself has suggested as much. In his speech declaring war on Wednesday night, he warned that “anyone who would consider interfering from the outside” will “face consequences greater than any you have faced in history” — a thinly veiled threat to nuke the United States or its NATO allies if they dare intervene.”