The current conflicts involving Russia, Ukraine, the U.S., NATO and Europe are complex.
The principle, however, is not. In fact, it was summarized on Monday by Deputy Secretary of State Wendy Sherman after meeting her Russian counterpart, Deputy Foreign Minister Sergei Ryabkov.
"We will not allow anyone to slam closed NATO's open-door policy, which has always been central to the NATO alliance," Sherman told reporters in Geneva. "We will not forgo bilateral cooperation with sovereign states that wish to work with the United States, and we will not make decisions about Ukraine without Ukraine, about Europe without Europe, or about NATO without NATO."
The "anyone" Sherman referred to in this case (most cases, actually) is Russia, whose repressive president, Vladimir Putin, has demanded deep concessions from the West to defuse a crisis he created regarding Ukraine.
It's not the first time. In 2014, Russia illegally cleaved Crimea and since then has deeply destabilized eastern Ukraine, resulting in a low-grade war with high numbers of casualties — at least 13,000 killed so far. Scores more could be killed if the already deployed Russian forces of more than 100,000 engage in a full-scale invasion of Ukraine. That's what is implicitly at risk if Russia's demands — already labeled as nonstarters — aren't met.
This includes, Ryabkov said, "iron, legal obligations, not promises, but guarantees" that Ukraine not join NATO. "This is a matter of Russia's national security."
Based on Putin's past and potentially future behavior, it would seem to be a matter of Ukraine's national security that it not be shut out by NATO, especially since it and Georgia were told by the alliance that they would eventually be able to join. Neither is likely to ascend soon, but that decision should — and if the West holds firm, will — be made by Ukraine and NATO, not its former and future oppressors in Russia.
Putin has made other demands, including curbing NATO's ties with former Soviet states and forbidding deployments of alliance troops on NATO members that joined the alliance after 1997.