The Baltic states fear a Russian invasion. They faced the same threat a century ago and failed to stop it. Historian Alexey Uvarov explains why the region could not defend itself against Stalin.

As Russia’s full-scale invasion of Ukraine enters its fifth year, experts and Western intelligence sources are increasingly warning that Russia also poses a growing threat to countries in the Baltic region. So far, the confrontation has produced only isolated incidents, such as drone incursions into these countries’ territory — but tensions are rising. Latvia, Lithuania, Estonia, Poland, and Finland increasingly need to consider how they would collectively defend themselves against a full-scale invasion from the east. The problem is not new to the region: 100 years ago, the Baltic countries also tried to join forces to protect themselves from militarily stronger neighbors. They failed to create an effective defense alliance. In this article for Meduza, historian and memory-politics expert Alexey Uvarov examines lessons from the Baltic region’s failed efforts to build an effective defense alliance.

The security order around the Baltic Sea has changed significantly since Russia’s full-scale invasion of Ukraine began. Finland and Sweden have joined NATO, while the Baltic states and Poland have accelerated their rearmament and efforts to strengthen the alliance’s eastern flank. Disputes within NATO over burden-sharing have also intensified: President Donald Trump’s administration is demanding that Europe rely more on its own resources and spend more on defense, while Europeans are increasingly debating whether they can still count on the same level of American involvement in the alliance.

This leaves the countries of the Baltic region facing an old question: To what extent can they ensure their own security, both independently and through regional cooperation, if outside guarantees prove less reliable than before?

One hundred years ago, Finland, Estonia, Latvia, Lithuania, and Poland tried to solve a similar problem. After World War I, they formed regional alliances, signed agreements, and drew up joint military plans. By 1939, however, these efforts had failed to produce a functioning system of collective defense. That failure illustrates the limits of a regional alliance without a powerful outside guarantor.

How did the countries of the Baltic region first try to form an alliance?

After World War I, the idea of such an alliance seemed entirely natural. A chain of independent states stretching from Finland to Poland had emerged from the former Russian Empire. Most had just fought the Bolsheviks, and their borders had yet to be firmly settled. Nor was there any certainty that Russia would remain weak for long. Latvia and its first foreign minister, Zigfrīds Meierovics, were especially active in promoting the idea of a “Greater Baltic Union.” Between 1919 and 1925, representatives from countries across the region held 15 conferences on cooperation.

The most ambitious attempt came in the summer of 1920 at a conference in the Latvian resort town of Bulduri. Representatives from Finland, Estonia, Latvia, Lithuania, and Poland attended. They discussed issues ranging from economic and diplomatic cooperation to the creation of a political union. On August 30, the participants even adopted a draft agreement establishing such an alliance. But the conflict that would dog every subsequent effort to unite the region was already apparent: the prospective allies could not agree among themselves. Lithuania refused to sign the agreement, and Poland and Finland later failed to ratify it.

The main obstacle was the Polish-Lithuanian conflict over Vilnius. In the fall of 1920, Polish forces commanded by General Lucjan Żeligowski seized the city, which Lithuania regarded as its capital. After that, it became nearly impossible to imagine Warsaw and Kaunas — Lithuania’s temporary capital from 1920 to 1940 — in the same defense bloc. Yet Poland remained an important partner for Estonia and Latvia in containing Soviet Russia. This created a paradox. On the one hand, the countries agreed that each was vulnerable to outside threats on its own. On the other, they could not agree on who posed the greatest threat or which countries they were prepared to defend together.

Still, they did not immediately abandon the idea of a broad alliance. In March 1922, the foreign ministers of Finland, Estonia, Latvia, and Poland met in Warsaw and signed a new agreement. It prohibited the parties from entering into treaties directed against one another and called for coordinated action in the event of an external threat. But it fell short of a full military alliance: if one country came under unprovoked attack, the others were required to adopt a “benevolent” attitude toward it and agree on further measures. The treaty did not require them to go to war.

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But even this agreement never took effect. It sparked fierce debate in Finland: most parties considered the new foreign policy commitments too risky, and Parliament refused to ratify it. Helsinki subsequently became much more cautious about proposed alliances with the Baltic states and Poland. In the years that followed, it increasingly turned toward neutrality and cooperation with the Scandinavian countries. Finnish politicians feared that joining a Baltic bloc might not make their country safer and could instead draw it into a conflict over its allies’ interests. The Warsaw Agreement never entered into force.

Rather than forming a single broad alliance, countries in the region began pursuing smaller alliances. Estonia and Latvia went the furthest. On November 1, 1923, they signed a defense treaty under which an unprovoked attack on either country required the other to consider itself at war and provide military assistance. This was a full military alliance, but it included only two small countries. Lithuania remained outside it, Finland kept its distance from formal commitments in the Baltic region, and the earlier plan for a broad alliance that included Poland effectively collapsed. By the mid-1920s, a unified defense bloc stretching from Finland to Poland no longer seemed realistic.

How the Baltic region shifted from a broad alliance to bilateral partnerships

Paradoxically, Finland, which had refused to enter a formal alliance with the Baltic states, soon began close, secret military cooperation with Estonia to prepare for a possible conflict with the Soviet Union. In February 1930, the Finnish and Estonian general staffs discussed jointly closing the Gulf of Finland with minefields and coastal artillery. On November 29, 1932, they approved their first joint military plan. In the years that followed, the two countries held joint coastal defense exercises and expanded cooperation between their navies.

The Finnish-Estonian plan was straightforward. The Soviet Baltic Fleet was based in the eastern Gulf of Finland, primarily around Kronstadt and Leningrad, and had to pass between the Finnish and Estonian coasts to reach the Baltic Sea. The two countries planned to stop it there. Coastal artillery would close the passage with gunfire, while minefields and submarines provided additional defenses. The legacy of the Russian Empire played an important role: before 1917, the empire itself had built the Peter the Great Naval Fortress system on both shores of the Gulf of Finland to defend the approaches to St. Petersburg. Now, some of those fortifications were intended to keep the Soviet fleet from leaving the gulf.

By the late 1930s, the cooperation had become extensive: the general staffs had agreed on a joint military plan, the two countries’ coastal defense forces held joint exercises, and coordination gradually expanded to include their navies. But the partnership had a weak point. But the plans were not backed by a mutual defense treaty that would commit Finland and Estonia to go to war on each other’s behalf. The two countries’ militaries had a clear idea of how they would operate together in a war with the Soviet Union, but no agreement ever formalized those commitments.

The Baltic and Little Ententes: Next attempts at regional alliances

The Baltic states returned to the idea of a broader alliance in the mid-1930s. On September 12, 1934, Estonia, Latvia, and Lithuania signed the Treaty of Understanding and Cooperation in Geneva, creating what became known as the Baltic Entente. On paper, this was an important step: the three countries pledged to coordinate their foreign policies and hold regular meetings of their foreign ministers. But it did not create a military alliance. The treaty contained no commitment to provide military assistance automatically in the event of an attack.

The reason was the same as before: even a decade and a half after gaining independence, the three countries had different views of the main threats to their security. For Lithuania, the conflict with Poland over Vilnius remained the central issue, while its dispute with Germany over Klaipėda was becoming increasingly acute. Estonia and Latvia did not want to tie their foreign policies to Lithuania’s territorial claims, and the Vilnius issue was explicitly excluded from the Baltic Entente’s joint commitments.

Their attitudes toward the Soviet Union also differed. Estonia and Latvia were much more wary of Moscow, while Lithuania saw the Soviet Union as a potential counterweight to Poland and Germany.

As a result, the Baltic Entente allowed the three countries to coordinate their diplomacy but did not answer the central question: What exactly would they do if one of them had to go to war?

A similar problem emerged farther south in the Little Entente, which consisted of Czechoslovakia, Romania, and Yugoslavia. Created in the early 1920s, the alliance was intended primarily to contain Hungary and prevent a Habsburg restoration. When Germany became the main threat to Czechoslovakia in the 1930s, Prague tried to extend the alliance’s commitments to cover a possible German attack. Romania and Yugoslavia refused. Alliances created to counter the threats of the previous decade proved poorly suited to the new circumstances.

Trial by fire: Why the Baltic states failed to stop the threat from the east

The regional alliances were put to the test just a few years later. After the Molotov-Ribbentrop Pact was signed and Poland was partitioned, the Soviet Union began pressuring the Baltic states to allow a Soviet military presence. Estonia was the first: under threat of force, it signed a mutual assistance treaty with the Soviet Union on September 28, 1939, allowing Soviet bases on its territory. Latvia and Lithuania agreed to similar treaties in October. Formally, the three countries remained independent, but their ability to pursue independent policies was significantly reduced.

Finland came next. Moscow demanded border changes on the Karelian Isthmus, the transfer of several islands in the Gulf of Finland, and a Soviet naval base at Hanko. Finland was prepared to make some concessions, but the two sides failed to reach an agreement. On November 30, the Red Army invaded Finland. The countries that had recently discussed their common security now found themselves in completely different situations: Finland was at war with the Soviet Union, while Estonia, Latvia, and Lithuania were forced to tolerate Soviet troops on their soil.

The contrast was especially stark in the relationship between Finland and Estonia. Not long before, their militaries had been preparing together to trap the Soviet fleet in the Gulf of Finland. Now, the Soviet Union was using bases in Estonia during its war against Finland: Soviet aircraft flew combat missions from these bases, while ships and submarines operated from Estonian ports. Yet the two countries’ military ties did not disappear entirely. Despite the Soviet military presence, Estonian representatives continued to secretly pass intelligence to Finland.

The Baltic Entente formally continued to exist. In December 1939, after the Winter War had already begun, the foreign ministers of Estonia, Latvia, and Lithuania met in Tallinn for another conference. There, they informally agreed to abstain when the League of Nations considered expelling the Soviet Union over its attack on Finland. In an account sent to Washington, an American diplomat cited the episode as evidence that the three countries had yielded to pressure from Moscow in their foreign policies.

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This tragic outcome brought a series of failed attempts to organize a regional alliance to a close. The countries had treaties, diplomatic mechanisms, and even fairly detailed joint military plans. But they never developed a shared understanding of the threats they faced, created a common planning mechanism, or, most importantly, decided in advance under what circumstances each would be willing to go to war for another. Even the Baltic Entente remained a tool for coordinating foreign policy rather than a military alliance.

The final test came in the summer of 1940. In June, the Soviet Union issued ultimatums first to Lithuania and then to Latvia and Estonia, sent in additional troops, and occupied all three countries. Moscow accused the countries, among other things, of turning the Baltic Entente into a military alliance directed against the Soviet Union, thereby violating the mutual assistance treaties they had signed in the fall of 1939. The Baltic states denied that such a military pact existed. The alliance that had proved too weak to ensure the three countries’ collective defense was ultimately used by Moscow as one of the pretexts for ending their independence altogether.

What historical lessons can be learned a century later?

The push for a regional alliance did not fail because the countries misunderstood their vulnerability or made no effort to cooperate. During the 20 years between the world wars, they held dozens of negotiations, signed several treaties, and even developed joint plans for a possible war. The problem lay elsewhere: their cooperation never produced a common understanding of precisely which threat the alliance was meant to deter. The Soviet Union remained the main potential adversary for Estonia and Latvia, while Lithuania was preoccupied with its conflict with Poland. Poland itself feared both Germany and the Soviet Union. Finland, meanwhile, increasingly looked to its Nordic neighbors and pursued neutrality instead of joining a Baltic alliance.

Nor could they resolve the more difficult question of who was truly prepared to fight for a neighbor. Estonia and Latvia made that commitment to each other, while the Finnish and Estonian militaries went so far as to develop detailed joint plans. But no common system stretching from Finland to Poland ever emerged. Ultimately, each country confronted the crisis alone: Poland was defeated and partitioned first; the Soviet Union then attacked Finland; and in the summer of 1940, it occupied and annexed the three Baltic states.

Finally, even closer cooperation could not eliminate the power imbalance between the smaller countries and their larger neighbors. A regional alliance could raise the military cost of an attack and make military operations significantly more difficult for the aggressor, but it could not guarantee that the member states’ own resources would be enough to sustain a prolonged war.

The Baltic region’s interwar history raises a question that remains relevant today: Is combining the forces of small and midsize states sufficient to ensure their collective security, or does a durable system of collective defense require commitments from major outside powers?