(CNN) -- Cheers in Moscow. Fear in Kiev. And jeers from the West.
When Russian President Vladimir Putin announced the annexation of Ukraine's Crimea region Tuesday and signed a formal decree, he made a major European crisis almost irreversible.
His nation's lawmakers wept and gave him a standing ovation in parliament as he barraged the West for what he described as its numerous betrayals. But in Western capitals, there was no applause. Governments imposed sanctions on Russian leaders and warned that's just the beginning.
Here's the rationalization for Putin's decision, and the reasoning for the West's derision.
Crimea rightfully belongs to Russia
Former Soviet leader Nikita Khrushchev gave Crimea to Ukraine in 1954. At the time, no one thought the Soviet Union would collapse, Putin said.
It did. And Crimea was handed over "like a sack of potatoes," Ukraine's Kyiv Post said.
Now the people have spoken, and they want to be a part of Russia, Putin said, referring to a hastily-called weekend referendum on separating from Ukraine.
"In our hearts, we know Crimea has always been an inalienable part of Russia," he said.
No, it doesn't
Ukrainian Prime Minister Arseniy Yatsenyuk called the annexation "a robbery on an international scale," one that his nation will never accept.
President Barack Obama and other European allies have accused Moscow of violating Ukraine's sovereignty and independence.
Crimea, which has an ethnic Russian majority, has long been a semiautonomous region within Ukraine. It had its own Parliament, but Ukraine had veto power over its actions.
"One country has come and temporarily stolen part of the territory of an independent country," Yatsenyuk said.
Russia had no choice but to act
Ukraine's new government, backed by the United States and European powers, prepared "to seize the state through terror and murders," Putin said. What was Russia to do? he asked.
"The main executors of this were nationalists, Russia-phobes and anti-Semites," he said. "Those people define what is happening today in Ukraine."
Russia saw a chance and pounced
International observers said Moscow saw its chance to annex a strategic territory and took it. The region is pretty significant: It still hosts the home port of Russia's Black Sea fleet.
Putin is "mimicking the fascists of the last century" by annexing Crimea, Ukrainian President Oleksandr Turchynov said.
And he has goals, some analysts say.
"His project for his third term as President is to gather in as many of his neighbors as he can to form a new Eurasian Union," said Angela Stent, a professor at the Georgetown University School of Foreign Service. "Ukraine is the key to that project. And Crimea is the key to Ukraine."
The annexation's legal
The Russian leader accused the West of "double standards" in its response to the Crimean crisis, citing Kosovo's split from Serbia. In 1999, NATO conducted a two-month bombing campaign to separate Kosovo's Albanian population from the rest of Serbia. The United States supported the breakaway.
"It's absolutely in favor of their own interests -- black today, white tomorrow," Putin said.
He said anyone who would allow Kosovo to split from Serbia and not Crimea from Ukraine would be showing "absolute cynicism."
The annexation's illegal
The United States said Russia's justifications for taking Crimea amount to an attack on Ukraine's sovereignty.
"President Putin today gave a speech rewriting history, and it only further put him on the wrong side of history," U.S. Secretary of State John Kerry said.
Preceding the 1999 NATO campaign, ethnic Albanians were being slaughtered. Crimea's ethnic Russians were not facing the same prospect.
The rest of Ukraine's safe
Even though there are Russian troops and vehicles along the border, Putin says there are no plans to take any more territories from Ukraine.
The rest of Ukraine's under threat
Ukraine stands at "the beginning of a very dangerous conflict, and we should do our best to stop this process," said Petro Poroshenko, a former foreign minister and a leading potential candidate for President.
"Several weeks ago, we had a guarantee that nothing (would) happen with the Crimea," he told CNN's Christian Amanpour. "Now under attack can be any country in the European Union, including other parts of Ukraine."
Russia will pay
U.S., Australian and EU officials imposed sanctions on more than two dozen Russian and Crimean officials. They include visa bans and frozen assets.
"President Putin should be in no doubt that Russia will face more serious consequences, and I will push European leaders to agree further EU measures when we meet on Thursday," British Prime Minister David Cameron said.
U.S. Vice President Joe Biden said Russia faces more than just sanctions. "We're talking about Russia putting itself on a path that undermines long-term confidence and creates obstacles for its full participation in the global economy," he said. "That path that they've placed themselves on does nothing to help the next generation of Russians compete and succeed in a world that will be led by the most dynamic and open economies."
But Stent said maintaining warm ties with the United States is not a priority for Putin. Russia's granting of NSA leaker Edward Snowden asylum clearly shows that.
"Guaranteeing and expanding the Russian presence in Crimea is much more important," she said.
Sanctions won't hurt
Russia's taking the threats lightly.
Vladislav Surkov, a Putin aide named in the sanctions, called it "a great honor" to be singled out for American punishment.
"We wait for sanctions," deputy Prime Minister Dmitry Rogozin posted on Twitter. The message included a smiley face and a picture of a black bear, vodka and a rifle.
Biographer Alexander Korobko said a country that can produce almost anything has no fear for sanctions. "It is absolutely not in the U.S. interest to impose sanctions on Russia, because who will take American astronauts to space if not us Russians?" Korobko asked.
And the sanctions are a good indicator of how far this battle will go -- or rather not go.
"The so-called smart sanctions ... in response to events in Crimea were an anti-climax and a confirmation of a total lack of any desire on the part of the West to take the fight with Russia any further," said Alexander Nekrassov, a former Kremlin adviser.
This means war
After a member of its military was killed and more captured when masked gunmen seized their base near the Crimean regional capital, Simferopol, Ukraine's defense ministry authorized its forces to open fire.
It warned that the crisis was shifting from political to military, and blamed it on Russia.
No one wants war
"If there were an armed conflict, neither the United States nor NATO would get militarily involved," Stent said. "And the result could be the dismemberment of Ukraine and its division into two states on either side of a new East-West divide."
Instead, the West should offer Ukraine's interim government financial support and encourage it "not to let itself be provoked into a war with Russia as Georgia was in 2008."
This will isolate Russia
It's not yet evident whether the sanctions will turn Russia into a pariah nation, but the U.S. has issued warnings to Moscow.
"Russia military intervention in Ukraine will only deepen Russia's diplomatic isolation and exact a greater toll on the Russia economy," President Barack Obama said.
Putin's popularity soars
Though condemned by the West, the Russian leader was at the height of his popularity hours after the annexation. Crowds gathered at the capital to sing and dance. "Vladimir, Vladimir, we love you!" one woman said. "We bow to you."
To some Russians, it symbolized a defeat against the West.