KIEV, Ukraine — The United States and the European Union have embraced the revolution here as another flowering of democracy, a blow to authoritarianism and kleptocracy in the former Soviet space. But successful revolutions, as the interim government here has been learning, are a lot harder to maintain than it can seem in the bright dawn of first victories.

The challenges for Ukraine's new leaders are many and varied. With President Vladimir V. Putin of Russia now openly intent on a military showdown over control of Crimea, the government faces a powerful test of Ukraine's territorial integrity. Demonstrations are growing in the Russian-speaking east of the country, underscoring the tenuous nature of the government's control there. Washington and Brussels, Kiev's only hopes at this point for the aid necessary to avert economic collapse, are scrambling to deliver and have shown no desire for an armed confrontation with Russia.

READ MORE: After Initial Triumph, Ukraine’s Leaders Face Battle for Credibility