When Vladimir Putin came to power in 1999, he immediately called on the Russian military.
"This was really his first act, to launch the war in Chechnya," said Angela Stent, who is director of Georgetown University's Center for Eurasian, Russian and East European Studies and who has met with Putin at an annual conference throughout his presidency.
The Russian troops eventually subdued the rebel fighters in Chechnya, a region inside southern Russia. Over the years, Putin has sent Russian forces on several combat missions abroad, including to the former Soviet republics of Georgia in 2008 and Ukraine in 2014, as well as to Syria in 2015.
Putin's military moves have brought sanctions and ostracization from the West. The Russian economy is weak, and Russia is often described as a "declining power."
But Putin, who has now been president or prime minister for 22 years, strongly disagrees. Russia's military remains a potent force, and Putin has repeatedly used it — or threatened to use it — to demonstrate that Russia is still a country to be reckoned with.
Russia has now massed some 100,000 troops on its border with Ukraine, though it's not clear whether Putin is planning another invasion of Ukraine or is just bluffing as a way to win political concessions.
Given his track record, though, Putin is being taken seriously.
"The Kremlin will stop only when it is stopped," said Ben Hodges, who was the commander of the U.S. Army in Europe when he retired in 2017 as a lieutenant general.
Hodges, who currently lives in Germany, has been observing the Soviet and Russian militaries since he was sent to Europe as a young Army officer in the 1980s.
"They haven't given up one inch," he said of Russia's military actions in recent years. "They've only continued to expand. Sometimes they use actual force. Sometimes they use the threat of force. It seems like we are always on the back foot, that they always have the leverage. We're always responding to them."
This month marks 30 years since the breakup of the Soviet Union, an event Putin has described as the "biggest geopolitical catastrophe" of the 20th century.
Stent says this drives Putin to pursue two clear goals: first, his insistence that Russia be treated as a major global power and, second, his opposition to Western influence, including NATO expansion, into what he considers his neighborhood.
"Putin has been determined, since he became president, not necessarily to restore the Soviet Union, but to get the West to understand and to accept the fact that this is a Russian sphere of influence," Stent said.
Putin likes to keep his opponents guessing. Last April, Russia massed troops on its border with Ukraine. Putin didn't invade, but the episode led to a summit between Putin and President Biden in Geneva in June.
Now, Biden is warning of harsh financial sanctions if Russia invades. Ukrainian President Volodymyr Zelensky says his country's military is much stronger than it was when Russia invaded in 2014, in part because of increased Western military assistance.
So what's the likely outcome this time?
Russian leaders say their country has no plans to invade and is free to place its troops anywhere it likes on Russian soil. But the rhetoric is running hot, and the tense conditions raise the risk of miscalculation.
"This all might be bluster on the part of Moscow, Washington and Kyiv, but all sides seem to have really dug in their heels," said Tim Frye, a Columbia University professor and the author of the book Weak Strongman: The Limits of Power in Putin's Russia.
Frye distinguishes between what were two separate Russian military operations in Ukraine in 2014.
In the first, Russia seized the peninsula of Crimea quickly and without any serious fighting. Russia remains in full control, though its annexation of Crimea has not been recognized internationally.
"Certainly one of the reasons why the Crimean annexation was so popular [in Russia] is that it was largely bloodless. It was a low-risk, high-reward operation," Frye said.
In the second, which happened just weeks later in 2014, Russia supported separatists fighting in eastern Ukraine. That conflict has turned into a stalemate, though sporadic skirmishes still break out, and some 14,000 people have been killed.
"Fighting in eastern Ukraine is something that is much more costly for the Kremlin. There's much less domestic support for this kind of fighting," said Frye.
He believes Putin would likely settle for a negotiated deal that gives him strong political influence in Ukraine — and doesn't involve an invasion.
Negotiations among the U.S., Russia and others are planned for the coming days. But there's no guarantee Putin will win concessions, and his aggressive actions have turned most Ukrainians against Russia.
"If he doesn't realize that he has really alienated the Ukrainian population by doing all of this, then he's really not getting very good feedback," said Stent.
Hodges says even though the Soviet Union may be long gone, many Russians still share Putin's belief that they should have strong influence in former Soviet states.
"If President Putin fell off his horse tomorrow, we would still be dealing with this for years to come," said Hodges. "So this is not just about him."
But for now, everyone is watching Putin to see what he does next.
Greg Myre is an NPR national security correspondent who was based in Russia from 1996 to 1999. Follow him on Twitter: @gregmyre1.
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