The war in Ukraine has sent shock waves through Eastern Europe, and nowhere more so than in the Baltics. The Kremlin’s aggression since Russia’s annexation of Crimea has blurred the lines of the impossible. Estonia, Latvia and Lithuania, all North Atlantic Treaty Organization member states, fear a Russian attack.

In tiny Lithuania the threat from Moscow feels so real that the country plans to reintroduce military conscription. Unlike Latvia and Estonia, Lithuania does not share a border with mainland Russia. To the south is Belarus, headed by Aleksander Lukashenko, Russian President Vladimir Putin’s puppet dictator. The Russian army is bolstering its bases there. To the west lies Kaliningrad, Russia’s heavily militarized exclave in northeast Europe.

Lithuania’s chief of defense, Jonas Vytautas Zukas, announced the plans for renewed military service. “A critical shortage of soldiers,” he explained, “prevents us from being properly prepared and poses a real threat to our national sovereignty.”

President Dalia Grybauskaite said restoring conscription was a “necessity” and Lithuania, with a population of almost 3 million, has “no other way to strengthen its army.” If parliament passes the bill, roughly 3,000 men between age 19 and 26 could be drafted into the army as early as this September.

One of Europe’s smallest militaries, the Lithuanian armed Forces now has 15,000 personnel. Since Lithuania joined NATO in 2004, it was largely prepared to contribute to any joint missions, such as Afghanistan or Kosovo, not for territorial defense. But Russia’s sharp revisionist turn has forced Vilnius to dramatically reconsider its security policy.

The return to conscription culminated a series of steps to prepare Lithuanians that the threat from Moscow is not imaginary. Fearing an incursion of Putin’s “little green men” — Russian soldiers who infiltrate foreign nations without insignia — Vilnius banned any wearing of military-style clothing without permission. Saturday, Berlin said that Lithuania was reportedly interested in buying tank howitzers. Last month, Lithuania’s defense ministry published a 98-page manual to gird citizens for the possibility of invasion, occupation and armed conflict.

After Russia’s annexation of Crimea, many security experts have warned that Moscow’s hybrid warfare could spread to the Baltics. But Marius Laurinavicius, a senior Lithuanian analyst at Vilnius’ Eastern Europe studies center, believes his country faces a real threat of conventional invasion from Kaliningrad.

“They [the Kremlin] need a corridor from Kaliningrad to mainland Russia,” Laurinavicius said, “just like they need one from Crimea to Donbas.”

Kaliningrad has long been an outpost for confrontation with the West. It was one key reason the Baltics joined NATO as late as 2004, five years after Central Europe’s post-communist states. Warning signs of the danger from the region were clear years before Russia’s Ukraine adventure.

In August 2013, for example, the Kremlin flaunted Kaliningrad’s armed might when Putin and Lukashenko raced their tanks in a massive military exercise near the Polish and Lithuanian borders. They shelled a 14th-century Prussian church.

But a scenario in which Russia invades the Baltics is only possible after Putin first tested his expansionist plans in Georgia and Ukraine. The European Union seems to believe that Moscow would never dare attack a NATO country. Laurinavicius, however, says the West is mistaken to view Putin through the prism of its own values. “Putin,” he said, “does not believe NATO will defend such, in his view, unimportant countries, risking nuclear confrontation.”

Other analysts warn that Putin could use ethnic Russian populations in the Baltics as a pretext for intervention. But Lithuania’s Russian population is far smaller than that of Latvia or Estonia. The country’s 200,000 Poles make up Lithuania’s largest ethnic minority. It is to them that the Kremlin has turned to.

The Polish minority’s political party, Electoral Action of Poles in Lithuania, is shrouded in controversy. Its leader, Waldemar Tomaszewski, slammed Ukraine’s Maidan protests, has compared the Crimea annexation to Kosovo and publicly wore the St. George ribbon, a Russian award for bravery established by the tsars in the early 19th century and now adopted by Russian-backed rebels in eastern Ukraine. Allied with Lithuania’s ethnic Russian party, the Russian Alliance, Tomaszewski has a seat in the European Parliament and finished third in Vilnius’ recent mayoral election. Even Warsaw, which has a longstanding disagreement with Vilnius over the rights of its compatriots in Lithuania, has grasped that Moscow is exploiting the Polish minority to put pressure on the country.

Tomaszewski’s strongly pro-Russian attitudes are a reminder that Moscow’s spies are working hard throughout the region. But the conflict with Putin is not just about Eastern Europe. Moscow’s destruction of the post-Cold War order tests the strength of Western institutions. In Eastern Europe, many look back to Munich 1938, when Western appeasement led to disaster. Though Britain, France and Italy agreed to cede parts of Czechoslovakia to Adolf Hitler’s Germany, it did not forestall war.

“We need to remember,” Alvydas Medalinskas, an analyst at Vilnius’ Mykolas Romeris University told me, “how much Munich increased the aggressor’s appetite.”

Nowhere are the consequences of these mistakes more visible than in the Baltics. Abandoned by the West into Soviet servitude, Lithuania’s long fight for independence has left many unhealed wounds. Today, the Kremlin’s spokesmen and Russian propaganda consistently undermine the sovereignty of the three Baltic countries. Many Russian intellectuals, who before the Maidan revolution had strongly stood up for the Baltics and Ukraine, are nowhere to be heard.

It was not always this way. The solidarity of Russian democrats with Lithuania was an important part of the country’s fight for freedom. Medalinskas remembers banners on Red Square in 1991 that read “Today Vilnius, Tomorrow Moscow.” In 2015, he struggles to find a common language with many of his Russian friends.

One of those Russian democrats in the fight was Boris Nemtsov, shot dead near the Kremlin last month. The threat to the Baltics grows with every day of Moscow’s aggression in Ukraine and sinister clampdown at home. Nobody knows what Putin will do next.

Lithuanians, meanwhile, are preparing for the worst.