Last week, before Vladimir Putin annexed the Ukrainian region of Crimea to Russia, I asked a leading Putinologist, Fiona Hill of the Brookings Institution, what the Russian president was likely to do.

“He’s on the offensive,” she said. “In his view, he’s got the advantage. He doesn’t seem likely to stop now.”

She turned out to be right. On Tuesday, Putin signed the treaty of annexation in a flag-decked Kremlin ceremony as crowds cheered outside in Red Square. In a defiant speech, the Russian president said the action merely restored Crimea to its motherland. “Crimea has returned home,” he told the crowd.

By tapping into the traditional nationalism of Russians and their desire to be seen as a great power, Putin has improved his domestic political standing, and he’s done it at a time when Russia’s economy has slowed to a crawl. A recent poll by the respected Levada Center put Putin’s job approval at 72 percent — well above, say, President Obama’s.

With that kind of cheering section, it seems unlikely the Russian leader will stop now. His most immediate goal may be to secure Crimea’s energy sources, most of which happen to be in eastern and southern Ukraine, which also have substantial Russian populations. But that won’t be all. Putin’s central goal as president, Hill said, is to restore Russian influence over as much of the territory of the old Soviet Union as possible, beginning with Ukraine.

Russia won’t necessarily try to annex more of Ukraine, but Putin is bent on ensuring that the country joins his planned Eurasian Union instead of the European Union. “This is his legacy,” said Hill, who coauthored the widely praised biography “Mr. Putin: Operative in the Kremlin.” “This is what his presidency’s about.”

That’s why Putin wasn’t willing to stand by as a rebellious Ukraine moved toward a formal economic association with the EU. And that’s why he will continue to exert pressure on both eastern Ukraine, where much of the population is pro-Russia, and on the understandably anti-Russia government in Kiev.

One possible next move would be for Russia to annex Transnistria, a self-declared separatist state on Ukraine’s western border. Transnistria broke away from Moldova, though its sovereignty has not been recognized by most countries, and now has close ties with Russia. “Keep your eye on that one,” Hill warned. “It’s another way Putin can create a problem for the government in Kiev.”

At its heart, the conflict in Ukraine is as much about Putin’s fears as his ambition. In Putin’s mind, he is acting to defend Russia’s interests against an assertive, expansionist West. (As recently as 2008, after all, NATO was moving toward making Ukraine a member.) He rejects the idea that every country should be moving toward both democracy and a Western-style market economy. To the Russian leader, democracy looks like chaos. And after the U.S. financial crash of 2008, “he doesn’t think the West is worth emulating as an economic model anymore,” Hill said.

In other words, Putin’s looking at the 21st century through the cold, wary eyes of a Russian realist, and he sees it differently than Western leaders do.

Take the recent threats of economic sanctions from Europe and the United States. Putin thinks the West will hesitate before imposing crippling sanctions on Russia’s economy because of Europe’s many financial interests in Moscow. (So far, he’s right about that.) And he thinks the West will tire of imposing sanctions before Russia feels any need to back down.

“His message is: We think you’ve been trampling our interests, and we have a higher threshold for pain than you do,” Hill said. She noted that Putin’s parents survived the World War II siege of Leningrad, when some Russians ate grass to fend off starvation - an episode Putin once referred to as evidence of his nation’s resilience under pressure.

Obama, German Chancellor Angela Merkel and their allies hoped threats of sanctions would deter Putin from moving troops into Crimea, but their threats had no effect. They hoped the imposition of limited, “proportional” sanctions might deter Putin from annexing Crimea, but that had no effect either.

What we have here is an asymmetrical problem: It’s more important to Putin and his people than it is to the West. For Americans and Western Europeans, Russia’s assertion of power is an outrage and a threat to our ideal of an international order, but it’s also a long way from home. For Putin, it’s the cure for Russia’s national resentments and the legacy he wants to leave as president. He’s betting that he can outlast any sanctions the West is willing to impose. He could well turn out to be right.

Doyle McManus is a columnist for the Los Angeles Times.