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.

These were well-telegraphed before Monday's meeting, as was the eventual U.S. response. "It was very much as expected; it was simply each party laying out their positions that I think are fairly well known. So I don't see that the talk will change the trajectory of the possibility for further Russian military expansion in Ukraine," Timothy Frye, professor of post-Soviet politics at Columbia University, told an editorial writer.

Frye, author of a recent book on Putin, "Weak Strongman: The Limits of Power in Putin's Russia," added that all parties — Russia, the West and Ukraine — have all "staked out very hard-line positions about what they're willing to accept." Accordingly, "it will take some creative diplomacy to avert an escalation of the crisis."

The U.S. seemingly attempted some of that creativity, including offering to broaden discussions on reinstating the recently abandoned Intermediate-range Nuclear Forces Treaty and, as Sherman stated it, "ways we can set reciprocal limits on the size and scope of military exercises and to improve transparency about those exercises."

Those are appropriate, productive areas of exchange, and may offer Putin an off-ramp from his threats. But the U.S. and its NATO and Ukrainian partners should be prepared for everything — a full-scale invasion, cyberattacks, a trumped-up "provocation" from Ukraine that invites invasion, or half measures meant to split the alliance.

President Joe Biden was right to signal that severe sanctions will be triggered if Russia invades Ukraine. And Sherman was right to correctly state that statesmanship on issues like the INF treaty and troop exercises would not be rapid.

"We must give diplomacy and dialogue the time and space required to make progress on such complex issues," she said. For his part, Ryabkov stressed that "we cannot afford any additional delays."

What Russia, Ukraine, Europe and the world can't afford is war. Accordingly, diplomacy — undergirded by the principles espoused by Sherman — is the best way forward.