Crimea's parliament voted to split from Ukraine and join Russia Thursday and its Moscow-backed government set a national referendum on the issue within 10 days.
The decision is a dramatic escalation of the crisis over the Ukrainian Black Sea peninsula.
President Barack Obama said that "the proposed referendum on the future of Crimea would violate the Ukrainian constitution and violate international law," in remarks at the White House Thursday.
Could Crimea actually split from Ukraine? Is there any legal precedent that could legitimize the move?
"This is a crisis situation," said Mark Almond, Oxford University historian and expert in post-communist countries. "In effect, the normal rules have broken down and neither the Russians nor the West can agree how to put it together."
Authorities in Crimea -- a semi-autonomous and largely pro-Russian peninsula in Ukraine -- have decreed a referendum on the issue for March 16.
Meanwhile, Russia's Duma is considering a bill that would allow it to annex the Crimean Peninsula, which is very likely to be passed, according to Masha Lipman of Carnegie Center in Moscow.
So in theory, Crimea could soon become another autonomous region in Russia, like Chechnya, Dagestan and North Ossetia. This means they would follow Russian legislation, use the ruble and become integrated into the Russian Federation.
As if to drive the point home, some Russian television stations began to show maps of Russia that included the Crimean peninsula on Thursday after the vote.
But, annexation could violate existing agreements on Ukraine's sovereignty. In 1991 after the fall of communism, Ukraine became an independent country and was promised territorial integrity. This was bolstered In 1994 under the Budapest Memorandum signed by Russia, the U.S. and the U.K., during which it gave up its nuclear arsenal in exchange for Ukraine's territorial integrity, among other things.
Is there any legal precedent?
International laws make it hard for independence-minded regions to split away and join other countries.
“Borders can only be changed by mutual consent of countries,” according to John Lough of the Russia and Eurasia Program at international think tank Chatham House.
Given that Ukraine's new government is vehemently against the referendum, calling it "illegitimate," it looks unlikely that it will give their consent. Obama's remarks Thursday reveal the U.S. position that the move would be a violation of international law.
But, though Ukraine's Prime Minister Arseny Yatseniuk said a referendum would have "no legal grounds at all," there is actual precedent for the decision based on a 1988 law that allowed for self-determination for Soviet republics.
After the U.S.S.R. dissolved at the end of communism, Russia was surrounded by a crescent of independent former Soviet republics.
"The republics of the Soviet Union genuinely broke away peacefully, including Ukraine itself," according to Oxford University's Almond.
The West used similar arguments after the break-up of Yugoslavia to justify Kosovo splitting from Serbia, Almond added — yet another precedent.
Does Russia really want to annex Crimea?
Despite its sometimes belligerent language, Russia is not interested in alienating the West and prompting damaging international sanctions, experts say.
It isn't only the West Russia is likely worried about. If Moscow does end up accepting Crimea into the Russian Federation, it risks alienating neighboring China, which is fighting its own secessionist movements and wants to help stamp out examples that might give them oxygen.
So the referendum for Crimea independence could be a way for the West and Russia to be seen to respect the will of the people, while de-escalating, said Almond.
Chatham House's Lough agreed.
"Judging by [President Vladimir Putin's] remarks earlier in the week at the press conference, it looks like he wants to keep to the root of legitimacy," he said. "A legitimate outcome surely would be for Crimea to have greater autonomy within Ukraine.”
Who are the losers if Crimeans split from Ukraine?
While most experts agree that the majority of Crimeans will support a move towards Russia, the region's minorities are clearly nervous.
Muslim Tatars — who for centuries dominated Crimea, but suffered terribly under Joseph Stalin — spoke out quickly and emphatically against the move.
Refat Chubarov, a leader of the Crimean Tatars, compared a Russian annexation to Hitler invading Czechoslovakia’s Sudetenland in 1938 on the pretext that he had to protect badly treated German-speakers there.
The Tatars, who have already said they would boycott the referendum, may have reason to be nervous: anti-Muslim and nationalistic feelings run high in Russia.