Armed men, believed to be Russian soldiers, stand outside the civilian port in the Crimean town of Kerch. The words read: "Port Crimea". REUTERS/Thomas Peter

Berlin - Ukrainian nationalists and Kremlin opponents are convinced that Russian President Vladimir Putin meticulously planned the current military operation in Ukraine's Crimean peninsula while all eyes were on the Winter Olympics in Sochi.

The arrival in Crimea of thousands of Russian-speaking men in uniform in recent days has led to the most serious crisis with the West since the breakup of the Soviet Union.

The Russian moves have led to a geopolitical conflict that few analysts felt possible in the 21st century. Russian nationalists are ecstatic, while the West seems to still be in shock days later.

There are parallels to the Cold War conflicts of old. But unlike in Hungary in 1956, Prague in 1968 or Afghanistan in 1979, most of the people living in Crimea greet the Russian's arrival with enthusiasm.

They consider the shadowy Russian-speaking security men in uniforms without insignia to be their “brothers” - just like in former Soviet propaganda.

In Crimea, the United States and the European Union face one of their gravest challenges of the decade. The US has threatened Russian with sanctions and attempted to isolate its former rival. US President Barack Obama must consider the Russian president's actions in Crimea a provocation.

Putin launched his military action not 24 hours after Obama had warned him against doing so. Obama now has to act, according to US diplomat Nicholas Burns.

“It's the most important, most difficult foreign-policy test of his presidency,” Burns told the New York Times.

The EU and Germany face difficult decisions over the Crimea crisis: While there are some calls for international sanctions against Russia now, whether they could be agreed on or even have the desired effect is questionable. Some governments might shy away from economic sanctions.

Russia is after all the EU's key supplier of natural gas - and it has ample foreign currency reserves. Russia also remains an important export market.

The conflict with Moscow over Crimea also threatens to complicate efforts to defuse international issues including the Syrian war and the dispute over Iran's nuclear programme, which depend on close cooperation between Russia and the US.

The Crimea situation comes six years after the Caucasus war in 2008 which led South Ossetia and Abkhazia to split off from Georgia. Russia intervened militarily, ostensibly to protect ethnic Russians.

There is concern that problems with Russian minorities could develop in other former Soviet republics down the line, including Moldova's Russian-controlled Trans-Dniestr region. While pro-Western forces in Ukraine have long sought closer ties with Europe, Kiev is still somewhat of a stranger to the EU.

And even its joint staging of the European Cup football by Poland and Ukraine in 2012 didn't serve to bring Ukraine any closer. Ukraine's perennial quarrels with Russia over gas prices have not made it many friends in EU capitals either.

And the return of jailed opposition leader Yulia Tymoshenko does not fill everyone with joy. Many blame the failure of Ukraine's Orange Revolution 10 years ago on her squabbles with her former ally Viktor Yushenko. Corruption and mismanagement going back decades have led Ukraine to the edge of financial ruin.

The West is very attractive to ordinary Ukrainians, who hope the West can help ease the country's financial problems. And while the West is trying to formulate a joint strategy for dealing with a confident Russia under Putin, the Kremlin quietly continues to pursue its Crimean project. Constriction is about to begin on a bridge from the Russian Black Sea Coast to Crimea.

This would be the first direct link between Crimea and Russia. Were the sparsely populated region bordering the Ukraine mainland to be blocked off, the Crimean peninsula would only be reachable from Russia.