No one knows exactly how or when Russia’s war in Ukraine will end, but the terms are likely to be disappointing to Kyiv and its Western supporters. If that happens, the next phase will feature a nasty debate over who was responsible. Some of the participants will be motivated by a genuine desire to learn from a tragic episode, but others will be trying to evade responsibility, shift the blame onto others, or score political points. It’s a familiar phenomenon; as John F. Kennedy famously quipped: “Victory has 100 fathers, and defeat is an orphan.”

There’s no need to wait for this war of ideas to erupt because some of the competing positions are already out there and others are easy to anticipate. I’m not going to offer a detailed evaluation of them here; this column is merely a handy check list of the competing explanations for why the war happened and why it didn’t go as most of us hoped.

No one knows exactly how or when Russia’s war in Ukraine will end, but the terms are likely to be disappointing to Kyiv and its Western supporters. If that happens, the next phase will feature a nasty debate over who was responsible. Some of the participants will be motivated by a genuine desire to learn from a tragic episode, but others will be trying to evade responsibility, shift the blame onto others, or score political points. It’s a familiar phenomenon; as John F. Kennedy famously quipped: “Victory has 100 fathers, and defeat is an orphan.”

There’s no need to wait for this war of ideas to erupt because some of the competing positions are already out there and others are easy to anticipate. I’m not going to offer a detailed evaluation of them here; this column is merely a handy check list of the competing explanations for why the war happened and why it didn’t go as most of us hoped.

Argument #1: It was a mistake for Ukraine to give up its nuclear weapons. According to some observers, the first big error was compelling Ukraine to give up the nuclear weapons it had inherited from the former Soviet Union in exchange for some toothless security guarantees. Had Kyiv kept its own nuclear arsenal, so the argument runs, it would have been free to pursue whatever economic arrangements and geopolitical alignment it preferred without having to worry about Russian military intervention. This argument—recently invoked by former U.S. President Bill Clinton—maintains that Russia would not have dared seize Crimea in 2014 or invade the rest of a nuclear-armed Ukraine in 2022 because doing so would have been too risky. There are technical objections to this argument (i.e., it is not clear that Ukraine would have been able to use the weapons even if they had remained in its possession), but it’s still a counterfactual worth pondering.

Argument #2: Inviting Ukraine to join NATO was a huge strategic blunder. In the 1990s, a who’s who of sophisticated strategic thinkers warned that NATO........

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