After the euphoria of a successful popular revolution, Ukraine's problems begin now. And they will be compounded by the competing tug of four great powers.

Russia under President Vladimir Putin won't easily let go of the economic reins that have kept Ukraine within Moscow's orbit. Ukraine depends on Russian natural gas and oil and on Russian markets for many of its goods. Around one-quarter of Ukraine's population are Russian-speaking and many feel strong cultural ties across the border.

Then there is the Crimean Peninsula, long a part of Russia and handed to Ukraine by Soviet leader Nikita Khrushchev (allegedly while drunk) more than 50 years ago. Thrusting out into the Black Sea, it contains the major Russian naval base of Sevastopol, which Russia leases.

For Putin, maintaining Moscow's influence in Ukraine is a major national security priority, above all to prevent it slipping into what he sees as the Western camp of the European Union and NATO. There may be some wiggle room, under which Ukraine might pledge not to join NATO if it was able to deepen its economic ties with the European Union.

But for Putin this is also about Russian politics. The example and courage of the pre-democracy demonstrators in Ukraine's capital of Kiev will hearten Putin's internal opposition. Whatever temporary boost Putin may get from the successful Sochi Winter Olympics -- and from Russia topping the gold medal table -- Putin must fear that the bells ringing out in Kiev for the fall of Moscow's ally Viktor Yanukovich could also be tolling for him.

The second great power involved in Ukraine's future fate is that reluctant and vague entity the European Union, which has never been known for a bold or decisive foreign policy. The European Union is slow to reach agreement among its 28 members, even slower to enact such policies and deeply hesitant of any step that might antagonize an important neighbor like Russia, from which the European Union imports much of its fuel.

Moreover, the European Union is suffering from enlargement fatigue, after embracing the former Warsaw Pact countries of Central and Eastern Europe. The two countries that most resemble Ukraine in economic backwardness and corruption are Romania and Bulgaria, by far the least successful of the EU new member states.

Even though Ukraine's new government of national unity looks to be dominated by pro-European democrats who want a future within Europe, the response of Europe is likely to be reluctant. Still focused on its own hesitant recovery from the financial crisis and still deeply nervous about the euro, the European Union isn't in a generous mood as it looks at the economic disaster zone that is today's Ukraine.

An emergency aid package was discussed at the Group of 20 summit in Australia over the weekend and EU Economic and Financial Affairs Commissioner Olli Rehn noted, "It will have to be measured in the billions rather than hundreds of millions."

Ukraine has to repay $12 billion this year of its total $73 billion foreign debt and its reserves have shrunk to $17 billion, worth about eight weeks of imports. Some EU officials have suggested to this columnist that Europe, the United States and the International Monetary Fund would need to assemble a package of around $20 billion and hope that Russia might be invited to contribute.

Only Poland and the small former Soviet republics of Estonia, Lithuania and Latvia are really keen to embrace Ukraine within Europe. German, France, Britain Spain and Italy place a higher priority on their relations with Russia than on the democratic hopes of Ukraine and shrink from the prospect of more millions of poor Eastern Europeans heading their way to seek work and perhaps welfare.

The United States, while emotionally and politically attached to Ukrainian democracy, also has to consider its more strategic relationship with Russia. The Obama administration would like Ukraine to be Europe's responsibility and has been impatient with Europe's timidity: as Assistant Secretary of State Victoria Nuland said in a leaked phone call to the U.S. ambassador in Kiev earlier this month, "F**k the Europeans."

There is a fourth great power involved in Ukraine's future: China. In December, Yanukovich, meeting with the Chinese leaders in Beijing, said the two countries were discussing $8 billion in Chinese investments in his country. Earlier this month, Chinese trade and business leaders were in Kiev talking multibillion-dollar investments, including a new port at Sevastopol.

It is a little known fact but China is the largest of all foreign land-owners in Ukraine, seeing its legendary fertile "black earth" as an important source of food for its increasingly food-strapped population.

Ukraine's biggest problem, however, remains internal. A popular democratic revolution based in Kiev's main square has succeeded before and then failed as politicians proved unable after their Orange Revolution of 2004-05 to build an effective economy nor to resolve their own internecine squabbles.

Maybe they have learned from their mistakes but the economy is in serious trouble, the Russian minority is not going away and their ranks are divided.

The weekend revolution only succeeded because the opposition on Parliament suddenly Friday gained an extra 68 votes as independents and defectors from Yanukovich's Regions Party joined their ranks. So some former Yanukovich supporters will be in the new government of national unity, along with the most worrying wing of the old opposition, the extreme and anti-Semitic right-wing nationalists who see the Regions Party as near-traitors.

The most influential wing of the old opposition, the Fatherland Party, has too many chiefs. Arseniy Yatsenyuk, the young technocrat and former central banker and foreign minister who currently leads it, faces a delicate relationship with the better-known former Prime Minister Yulia Timoshenko, newly freed from prison. And they each have a rival in the far more charismatic Vitali Klitschko, the former champion boxer, leader of the Ukrainian Democratic Alliance Reform party.

The revolution may be over but its heirs still have to make it work, while dealing with the competing interests and roles of the great power neighbors. Putin won't easily let go of Moscow's traditional influence, while Europe's inclination and will to take Moscow's place is uncertain, even as Washington tries nudging them to do so.