London(CNN) The prospect of an imminent Russian invasion of Ukraine has heightened alarm in the region, threatening to plunge the country's 44 million inhabitants further into the grips of conflict.
But a move by the Kremlin would also ripple far beyond the two nations' shared border.
Experts fear it could usher in a new era of uncertainty in eastern Europe, disrupt supply chains and the global economy, and force a shift in geopolitical influence that damages the credibility of the West.
These fears could yet be averted. The Ukrainian government is downplaying the immediate risks of a full-scale invasion, even as officials on all sides scramble to find a diplomatic solution of a standoff that the Biden administration warns is precariously close to war.
If an incursion does occur, it is unclear what form it would take -- and predicting the intentions of Russian President Vladimir Putin is a notoriously unwise exercise. "Any contemporary warfare would be horrifying, but there are gradations to the horror," said Nigel Gould-Davies, a former British ambassador to Belarus who is now senior fellow for Russia and Eurasia at the International Institute for Strategic Studies (IISS) think tank.
The effectiveness of a NATO-led response is also crucial in determining how long and far-reaching the impacts of any invasion would be, analysts agree.
But any Russian move would carry a test of Western nations' resolve and pose a series of economic and security uncertainties.
"This is easily the most serious security crisis in Europe since the 1980s," Gould-Davies said.
"Russia and the West have disagreed so fundamentally on worldview and that fundamental disagreement has been swept under the carpet for years," added James Nixey, director of the Russia-Eurasia program at London-based think tank Chatham House.
"Now Russia has decided it's going to up the ante," he said. "It is a real-world problem that has global implications."
As the threat of a Russian move into Ukraine has grown, so too has the volume of the West's rhetoric.
US President Joe Biden told CNN Tuesday there would be "severe consequences" over any Russian invasion. British Prime Minister Boris Johnson said the country would contribute to any new NATO deployment in the wake of an attack, while French President Emmanuel Macron said the "the cost will be very high" if Putin decides to move.
But the "scale of the global reaction depends on the extent of Russia's insertion into Ukraine," Nixey said. He added that while many observers are cautiously optimistic that an all-out war will be averted, "I've been wrong before -- as most Russia analysts have."
The most immediate consequences beyond Ukraine would be felt in the eastern European and Baltic states which would find an openly bellicose Russia on their doorsteps.
"Ukraine borders several NATO states. There will be a great deal of concern that this is not just something happening nearby that could have spillover effects -- but that their security would be threatened," Gould-Davies said.
"If Russia is allowed, or not discouraged from, re-drawing borders yet again, then quite clearly Russia will take lessons from that itself -- where next?," added Nixey.
Much would then depend on the NATO response, and countries that could find themselves in the firing line would quickly notice an increased troop presence. As many as 8,500 US troops have been put on heightened alert for a possible deployment to eastern Europe, Pentagon spokesman John Kirby said Monday. Three US officials familiar with the discussions also told CNN that the United States and allies could send extra deployments to Romania, Bulgaria, and Hungary in the coming days.
Ukraine is not a NATO member, and the alliance would likely not send soldiers into the country. But following an incursion, a heavy troop presence would likely remain along Europe's eastern rim for as long as Russia held Ukrainian land -- a prospect that would rekindle memories of a Cold War-era barrier splitting east from west.
"There is going to have to be a response all along that NATO front line that acts as a deterrent ... and you have to have a whole war-fighting strategy around that," said Neil Melvin, director of international security studies at the Royal United Services Institute (RUSI).
"In Europe, this would change things enormously -- because we're so far from thinking in those terms," he added. Melvin predicted that nations would require "large enough forces to fight for a long period, to bring in new forces from the US, [and] to fight cyber dimensions."
"It's going to be a huge shift."
The economic fallout of an invasion is wrought with unknowns, but there are several possible knock-on effects that have worried experts since the buildup of Russian troops near the Ukrainian border first became clear.
Most directly, a disruption to Ukraine's agricultural production could have a direct impact on food supply.
The country is one of the world's four major grain exporters -- it is expected to account for around a sixth of the world's corn imports in the next five years, according to projections by the International Grains Council -- so a direct hit to its production and output could impact the supply of certain foodstuffs.
But more concerning is the wider potential impact on energy supplies, and the consequences of tough Western sanctions on Russia that would be expected after an incursion.
"If you're talking about a major conflict [involving] one of the biggest energy suppliers in the world -- and a major transit country to the rest of Europe -- then there can't not be significant impacts on energy markets," Gould-Davies said.
Russia provides around 30% of the European Union's natural gas, with supplies from the country playing a vital role in power generation and home heating across central and eastern Europe.
It has already been accused of exploiting that reliance; the International Energy Agency said Wednesday that Russia has contributed to an undersupply of gas in Europe by reducing its exports, and in recent months the country has put supply pressure on Moldova as well.
"We've seen Russia in recent months exploit and exacerbate the problems of global energy supply and higher prices," Gould-Davies added. "Could they contemplate the cost of something much more serious than this?"
Inflation in energy costs has already hit millions of homes in Europe -- in Britain, consumers will pay roughly £790 ($1,075) more to heat and light their homes this year, according to Bank of America -- and conflict in eastern Europe could spark or deepen cost of living crises in several countries.
One worry in Europe is that Russia would indeed be willing to handle a rupture with the European market, given its gradual pivot of gas and coal supplies to China in recent years.
An acceleration in that shift would cause "an enormous jolt on [Europe's] economy, because they're going to have to do something else," said Melvin. This could potentially stall plans for a nuclear phase-out in parts of the continent if nations are forced to frantically reach for energy alternatives.
The Biden administration has been conducting contingency planning to shore up Europe's energy supplies should Russia invade, anticipating gas shortages and a shock to the global economy, senior administration officials said Tuesday.
The EU is meanwhile working on a "wide array of sectoral and individual sanctions" in case of further Russian aggression, according to a European Commission statement that followed a virtual meeting with the leaders of the US, United Kingdom, Italy, France, Germany, Poland, the EU and NATO. Biden told CNN he would anticipate "significant economic sanctions."
Analysts generally expect a wide-ranging package of sanctions that could hit major Russian banks, the oil and gas sector, and technology imports. But the effects on Europe and the rest of the world would be felt, too.
"Any time you impose sanctions, you impose great costs on the target -- but you also have the risk of blowback harms on yourself and on your friends and allies," said Nathan Sales, an acting undersecretary for civilian security, democracy, and human rights at the US State Department during the Trump administration.
And while targeted sanctions on Russian individuals and companies have been relied on since Russia's invasion of Crimea in 2014, there is still "a substantial investment relationship" between the country and the West that could be ruptured, Melvin said.
"The question now is how much further would those sanctions go, and how much more isolated the Russian economy would become," he added.
Experts said the reverberations of an incursion, and more pertinently the strength of the Western response, will be felt worldwide. Some fear that any Russian move that it could chalk up as a victory could encourage other nations engaged in border disputes.
"China will be watching carefully for lessons that it can draw about Western resolve," Gould-Davies said. "The Taiwanese are going to draw lessons from that -- as is anybody in a border despite, living next to a vastly superior leader," agreed Nixey. Taiwan and mainland China have been governed separately since the end of the Chinese civil war more than 70 years ago, but China's ruling Chinese Community Party (CCP) sees the island as part of its territory and has not ruled out military force to take it.
That context is underscoring a sense in some quarters that the US response to the Ukraine crisis could dictate how it is viewed around the world for a generation.
"We would be seeing knock-on effects for years and maybe decades to come" if Russia orchestrates a successful move, Sales said. "That is going to tell dictators around the world that the US is a paper tiger."
He cited "rogue regimes like North Korea and Iran" as other nations that could seek to capitalize on such an outcome. But Sales added there also exists "a scenario where the US and NATO come out of this crisis with their credibility enhanced," should a strong response initiate a Russian climbdown.
Should lengthy tensions follow a Russian incursion, a debate could also be renewed in the US about what role the country should play in Europe. "They have a very stark political divide now between a global policeman role, which Biden has advocated, or the other camp that we only do what's in the US interests," said Melvin.
Though many implications of a Russian move into Ukraine remain far from certain, there is one thing experts can agree on. "In international politics, everyone is always watching everyone else," Gould-Davies said.