KIEV — In 1993, the late Harvard political scientist Samuel Huntington proposed that “the principal conflicts of global politics will occur between nations and groups of different civilizations.” His theorythat the world was divided into potentially warring civilizations — and later, his book on the topic — have been denounced by legions of critics, mainly on the liberal side. But it had and has retained one group of unlikely fans: Russian nationalists.

They saw in his definition of “Slavic-Orthodox culture” (including much of the former Soviet Union and reaching deep into East-Central Europe) a confirmation, albeit from a surprising quarter, of their own view of the world. That is, that Russia is and must remain the central and organizing power of a collection of states that history, religion and culture had predisposed to unity, and to a distinctly separate identity from a West that would devour them behind a front of “spreading democracy.”

President Vladimir Putin of Russia is an ardent Huntington-ite. His much quoted view that the collapse of the Soviet Union was the greatest geopolitical tragedy of the 20th century signaled a deeply felt loss of a world in which Russia ruled not so much by force but by cultural and political leadership. In such a view, the nations that comprise that civilization are less important than the civilization itself. For a Slavic-Orthodox state to shift to the West would not be a choice, but a betrayal of the bloc’s essence.

In a few weeks, the state that lives on the fault line between Huntington’s Western and Slavic civilizations will have to make what James Sherr, one of its foremost Western observers, calls “a civilizational choice.” Sherr writes that the European Union is about to offer Ukraine an Association Agreement and trade pact that will “provide tangible mechanisms of integration with the EU” — an open invitation to shift the core of Ukraine’s statehood to the West.

There is another offer on the table, from the east. Russia has constructed a Eurasian Customs Union (ECU) that takes in Belarus to its west and Kazakhstan to its south. The ECU is said to be both rules-based and relatively efficient, “harmonized with international norms and the World Trade Organization regime.” Russia is not just inviting Ukraine to join the ECU — it is seeking to frighten it into it, instituting the beginnings of a trade embargo to show what might happen on a bigger scale if its offer were spurned, and threatening higher prices for the gas it supplies to its neighbor.