WASHINGTON - The U.S. 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.
Biden's analysis, delivered during a White House news conference in January, spelled out in stark terms why Americans should care about the fate of an eastern European nation that's roughly the size of Texas and is known for golden sunflowers, the Chernobyl nuclear disaster and being the spark for Donald Trump's first impeachment saga.
The latest conflict is rooted in Russian President Vladimir Putin's desire to re-establish the influence that Russia wielded under the Soviet empire, foreign policy experts say. The U.S., in turn, wants to keep Russian aggression in check while working to strengthen a struggling democracy that has become more closely aligned with the West.
The U.S. has already spent billions of dollars to help Ukraine build up its military defenses, an investment that's likely to escalate dramatically if Russia invades. While Biden has said the U.S. would not send troops to help defend Ukraine against Russian forces, he said the U.S. would likely send more American forces to other eastern European countries, including Poland and Romania.
The spark for a wider war?
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.
If Russia is allowed to invade, occupy and annex its neighbor, "that's an inherently very unstable international system, which will affect America's security and its prosperity," Conley said.
A Ukrainian government minister warned Britain's Sky News in December that a full invasion of Ukraine would spread conflict around Europe and could even trigger World War III.
"It is unpredictable as to what will happen," agreed William Taylor, former U.S. ambassador to Ukraine. He noted that throughout history, conflicts often start small with an assassination or a strike on one country that then spreads to other parts of the world.
Russia 'won't stop' with Ukraine
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.
"If the Russians succeed in reestablishing a sphere of influence or of dominating Ukraine, they won't stop there. They will continue," Taylor said.
"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.
Other U.S. 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.
"NATO and the U.S. credibility are on the line," said Will Pomeranz, acting director of the Wilson Center's Kennan Institute, a think tank dedicated to Russian and Eurasia research. "And if they fail, that will be taken by China and other adversaries as an unwillingness by the West to defend its interests."
More: 'There are no minor incursions': Ukrainian president rebukes Biden over remarks on Russian invasion
Putin's power and legitimacy
Tensions between Russia and Ukraine have erupted frequently in the three decades since Ukraine declared its independence.
Ukraine, which has a population of 44 million, has deep historical and cultural ties to Russia. The two countries share the same language and a 1,200-mile border. Many Ukrainians work in Russia. Russian companies are among the largest investors in Ukraine.
But Ukraine has forged closer ties to the West since the fall of the Soviet Union. In 2008, it sought - and was promised - membership in the NATO alliance. Though that membership has never been granted, the prospect of a bigger, stronger NATO has rattled Putin, who still sees Ukraine as a part of Russia.
Ukraine, Putin insists, must never be granted NATO membership.
In 2014, Russia annexed the Crimean peninsula, a swath of Ukraine territory between the Black Sea and the Sea of Azov. 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 U.S. and its allies view the annexation as illegal and imposed sanctions in response. Last year, the U.S. sent more than $400 million in military aid to Ukraine; since 2014, the U.S. has provided about $2.5 billion in assistance to the country.
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.
Putin denied that he was plotting to invade the country again. But the U.S. and its NATO allies didn't believe those denials, citing Putin's long history of refusing to accept Ukraine's sovereignty.
Analysts say Ukraine poses no defensive threat to Russia, so Putin's designs on the country have more to do with his long-held ambitions of expanding Russia's influence and returning to what he views as the greatness of the Soviet empire.
As Zbigniew Brzezinski, who served as President Jimmy Carter's national security adviser, once said: "Without Ukraine, Russia ceases to be an empire. But with Ukraine suborned and then subordinated, Russia automatically becomes an empire."
"This is all about Mr. Putin's power, his legitimacy and maintaining it," Conley said.
Putin's legacy would be much more secure if he created a modern thriving economy that benefitted all Russians, Conley said. Instead, he has presided over a decade of steady economic decline in his country.
"While he has hypersonic cruise missiles, the Russian people are not getting the services and the standard of living that they deserve," Conley said.
What Putin fears most, she said, is that Russians will see the Ukrainian people living in a free, democratic society where the results of elections aren't determined in advance and citizens are allowed to speak their minds.
"The greatest threat to Russia is a free and thriving Ukraine," Conley said. "Because if Ukrainian people can experience it, why can't the Russian people experience it?"
More: Biden warns Putin of harsh consequences if Russia invades Ukraine
After Russia invaded Georgia, another former Soviet republic, in 2008, the U.S. sought to reset its relations with Moscow.
"We got back to normal, and the message that sent was we get over it," Conley said. "Now we're into much more serious territory."
Michael Collins covers the White House. Follow him on Twitter @mcollinsNEWS.
Contributing: Courtney Subramanian and Deirdre Shesgreen
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This article originally appeared on USA TODAY: Russia and Ukraine: Why Americans should care about conflict