Striking the right balance between relations with the West and relations with Russia has always been Ukraine’s central foreign policy challenge. Ukraine’s leaders have sought to have it both ways: to grow relations with the United States, European Union and NATO while also trying to maintain a stable relationship with Russia.

Kyiv pulled off this balancing act in the 1990s. Its first steps to engage the West did not appear to threaten key Russian interests. Boris Yeltsin accepted Ukraine as an independent state. Vladimir Putin, however, is not Boris Yeltsin, and today’s Russia is not the Russia of the 1990s. The current Russian president wants to prevent Ukraine from slipping too far toward the West, has significant leverage over Kyiv and is prepared to use it. The Russians’ spectacularly ill-timed February 26 decision to launch a snap military exercise is not an encouraging sign, nor are the February 27-28 developments in Crimea.

Ukraine regained its independence following the Soviet Union’s collapse in 1991. While a small minority of ardent Ukrainian nationalists wished that Russia would simply disappear, Kyiv had no realistic divorce option. The Soviet system left the Ukrainian and Russian economies thoroughly intertwined. The Ukrainian energy sector remained hugely dependent on Russia for natural gas, oil and fuel rods for its nuclear reactors.

Historical and cultural links bound the two as well. For most of the 350 years leading up to 1991, Ukraine had been part of Russia’s empire. Breaking up was hard to do. A senior Russian diplomat told me in 1994, “Up here (pointing to his head), I understand Ukraine is an independent country, but down here (this time pointing to his heart), it will need more time.”

Such sentiments—and Russian nationalist claims to Crimea—fueled the Ukrainian leadership’s worries about a domineering Russian neighbor. Kyiv deliberately built relations with the West as a counterbalance. In the mid-1990s, the Ukrainian government concluded a strategic relationship with the United States, a partnership and cooperation agreement with the European Union, and a partnership arrangement with NATO.

These yielded benefits. U.S. participation in a trilateral dialogue with Ukraine and Russia brokered a deal that moved 2,000 nuclear weapons out of Ukraine—on better terms than the Ukrainians could have negotiated bilaterally. Warming relations between Ukraine and NATO prompted Moscow to settle long-standing differences with Kyiv over basing part of the Russian Black Sea Fleet in Crimea.

In the late 1990s, President Leonid Kuchma often described his foreign policy as “multi-vector,” reaching out to Russia, Europe and the United States. Russian officials appeared relatively relaxed about the westward vector. Kuchma expressed interest in joining the European Union, but that was clearly not a realistic prospect any time soon.

With regard to NATO, Kyiv sought cooperation, not membership. At a conference in 1999, Volodymyr Horbulin, secretary of the National Security and Defense Council and Ukraine’s smartest strategic thinker, expressed appreciation for NATO’s “Open Door” policy. Horbulin suggested that Ukraine might someday aspire to membership, but he described that option as plainly out of reach until NATO could command support from a large segment of Ukrainian elite and public opinion.

As for Russia, it was in disarray for much of the 1990s. Boris Yeltsin also made things easier. As erratic as he could be, and though he seemed to have little patience for his Ukrainian counterparts, Yeltsin accepted Ukraine’s sovereignty and independence—and the concomitant right of the country to make its own foreign policy choices. (In December 1991, Yeltsin had joined with his Ukrainian and Belarusian colleagues to proclaim the end of the Soviet Union and establishment of the Commonwealth of Independent States.)

Much changed with the end of the 1990s. Ukraine’s ambitions for its westward vector grew. And Vladimir Putin replaced Yeltsin as Russia’s president in 2000.

Putin has his own ambitions. He does not seek to rebuild the Soviet Union, even though he once famously termed its collapse the greatest geopolitical catastrophe of the 20th century. While perhaps sentimental about the USSR, Putin is a pragmatist.

Putin wants a sphere of influence, which he regards as an important aspect of Moscow’s great-power status. He expects neighboring countries to defer to Russian interests on major issues. Given its size and historical links to Russia, Ukraine is the prime target. Putin has sought—so far without success—to bring Ukraine into the Moscow-led customs union with Belarus and Kazakhstan.

A Ukraine moving toward the West seriously threatens Putin’s geopolitical construct. Moreover, he strives to appear to his domestic political base as a strongman and protector of Russia’s national interests. “Losing” Ukraine would undermine that carefully cultivated image.

Putin thus has responded very differently than Yeltsin to Ukraine’s pursuit of its westward vector. In January 2008, Ukrainian President Victor Yushchenko requested a membership action plan (MAP) from NATO. A few weeks later, Putin stood next to Yushchenko at a Kremlin press conference and calmly threatened to target nuclear missiles on Ukraine. The MAP request failed to win consensus support at the April 2008 NATO summit in Bucharest.

Fast forward to 2013. Ukraine, now under President Victor Yanukovych, neared signature of an association agreement with the European Union, which includes a free trade arrangement. Its full implementation would prepare the ground for a future EU membership bid—and pull Ukraine irretrievably out of Moscow’s orbit.

Putin accordingly cranked up the pressure. Last summer, Russian customs inspectors began to block the import of Ukrainian goods. Kremlin officials threatened all manner of financial ruin should Kyiv go forward with signing the agreement.

The threats worked. Yanukovych suspended the association agreement process and instead accepted Putin’s gifts of a $15 billion credit line and cheaper gas. But the European Union exerts a powerful pull. Tens of thousands took to the streets of Kyiv in November in protest. Stoked by anger over brutal police tactics, the protest swelled to the hundreds of thousands, ultimately bringing down the Yanukovych regime.

The new government in Kyiv supports the EU association agreement. Seen objectively, a Ukraine that is integrating with the European Union and at the same time maintaining a full range of political, economic and commercial relations with Russia should not pose a threat to Moscow. The European Union is not NATO. But Putin views this through his own prism and seems to regard it as a menace.

Unfortunately for Ukraine, the Kremlin has significant leverage over it, including cancellation of the credit line, trade sanctions, a gas price hike and even a gas cut-off. Economic sanctions would hurt the fragile Ukrainian economy, and Russia has resorted to such sanctions in the past. While separatist sentiments in eastern Ukraine are often overstated, the Russians appear already to be exploiting them in Crimea, the one region in Ukraine where ethnic Russians constitute a majority of the population.

This means that Ukraine’s new and untried government faces a more difficult challenge than any of its predecessors in maintaining its East-West foreign policy balance. As Kyiv pursues its relationship with the European Union, it also has to cope with a Russian policy that is designed to add to its burdens, when the government already confronts so many domestic tests.