was still deep in diplomatic discussions with Russia over the crisis in Ukraine when President Joe Biden succinctly summed up what’s at stake.

Another Russian invasion of the former Soviet republic would be “the most consequential thing that’s happened in the world, in terms of war and peace, since World War II,” Biden said.

Since Ukraine declared its independence from the Soviet Union in 1991, it has served as a buffer between Russia and the West, one whose security and stability could have ramifications for Europe and beyond.

“In many ways, Ukraine tells us about the future of the international system,” said Heather Conley, president of the German Marshall Fund, which promotes cooperation and understanding between North America and Europe.

A Russian invasion of Ukraine would spread fear across the region and would almost certainly lead to a further buildup of NATO forces in other eastern European countries, foreign policy experts  warn.

“The Poles and the Romanians, the Czechs will be very concerned as they see Russian tanks coming west from Russia into Ukraine toward them, and they will ask for reinforcements from the United States,” he said.

A successful Russian invasion of Ukraine, Taylor said, could embolden Russia to be more aggressive in other arenas – such as cyberattacks, election meddling and influence campaigns designed to undermine Western democracies.  .

adversaries also will be watching to see whether the Biden administration and its NATO allies will follow through on their warnings to answer a Russian invasion with devastating economic sanctions and additional shipments of weapons to Ukraine and other eastern European countries.

More: 'There are no minor incursions': Ukrainian president rebukes Biden over remarks on Russian invasion.

Russian operatives and separatist fighters have since launched attacks on eastern Ukraine, and the Kremlin continually works to undermine the country’s sovereignty militarily and in other ways.

The stage for the latest clash was set late last year, when Russia deployed more than 100,000 troops along Ukraine’s eastern border, raising alarms that another invasion was in the works.

As Zbigniew Brzezinski, who served as President Jimmy Carter’s national security adviser, once said: “Without Ukraine, Russia ceases to be an empire.

“While he has hypersonic cruise missiles, the Russian people are not getting the services and the standard of living that they deserve,” Conley said.

“The greatest threat to Russia is a free and thriving Ukraine,” Conley said.