Nations bordering Russia or Ukraine made an extraordinary, in terms of financial cost, effort to assist Ukraine during the first six weeks of the war. For example, tiny Estonia (population 1.3 million) spent about .8 percent of its annual GDP to support Ukraine during those six weeks. Most of the aid went to processing and hosting Ukrainian refugees fleeing the Russian attacks on their homes. Estonia also contributed some weapons. Estonia has only 6,000 active-duty troops but can mobilize trained reserves for a wartime strength of 60,000. The other two Baltic States, especially southern neighbor Latvia and below that Lithuania, which borders Poland and Belarus, have similar defense policies. Estonia and Latvia border Russia. Poland shares a long border, and history, with Ukraine. Poland has population six times larger than all three Baltic states and spent five times more during those six weeks on Ukrainian aid than all three Baltic states. Poland and the Baltic States know they are next if Russia succeeds in Ukraine. All four of these nations share a distrust of Russia and a long history of Russian aggression and occupation. Before Russia began attacking Ukraine in 2014 Russia had a per capita GDP half that of the Baltic states and Poland, whose economic success after 1991 inspired Ukraine to look to the EU (European Union) and NATO rather than domination by Russia. Since the 2022 Russian invasion, the unprecedented economic sanctions have reduced Russian per-capita GDP even further. Ukraine has also suffered economically but knows that if they survive the war with Russia, they can rebuild and achieve a GDP similar to their neighbor Poland, which has about the same population.
Every NATO member has somewhat different defense plans but the one thing all have in common is the ancient threat from the Russian Empire. While the larger NATO members (U.S., Britain and France) have nuclear weapons, the smaller ones have to be more creative in dealing with the Russian threat. The smallest and most exposed members of NATO are the three Baltic States: Estonia, Latvia, and Lithuania. Together these three nations have a population of only six million. Russia has over 140 million and an increasingly open desire to regain its valuable Baltic territories and other recently (1991) lost portions of the empire.
The Baltic States have long been fought over because, like most coastal areas, the Baltic States were always more prosperous than inland areas because of seaborne trade and fishing, in addition to farms inland. Poland, Sweden and Germany were a threat to what is now the Baltic States over the last thousand years, but since the 1700s another threat has been Russia, and still is.
Once the Soviet Union fell apart in 1991 many Russian neighbors feared a revival of the traditional Russian aggression and empire building. Poland joined NATO in 1999 and in 2004 Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia did the same, putting parts of the former Soviet Union (Estonia, Latvia and Lithuania) within NATO and on Russia’s border. Many Russians did not like this, for Russian policy since 1945 has been to establish a "buffer" of subservient (preferably Russian occupied) countries between Russia itself and the rest of Western Europe (especially Germany). This attitude is obsolete in a practical sense but old habits die hard.
In the 1990s the new post-communist Russian government said it was willing to work with NATO in areas of mutual benefit but that did not work out. Now there is a state of undeclared war between Russia and NATO. These new NATO members are more worried about renewed Russian aggression than the original NATO members (the U.S. and Western Europe). The nations of “east NATO” are asking for more presence by troops from “west NATO.” Some of the eastern members (especially Poland and the Baltic States) have called for the permanent basing of U.S. troops on their territory. The smaller states Estonia, Latvia, and Lithuania believe Russia could overrun them in two days and senior NATO military commanders openly agree. Russia considers such talk more evidence of NATO aggression against Russia. The Baltic States have heard this kind of talk from Russia before and want to avoid the usual outcome.
All three Baltic States have adopted similar defense plans based on that long used by Switzerland (and later Sweden and Israel). This “total war” mobilization system expected every citizen to be prepared to resist an invader. In the last century this has meant conscription of all able males (and even some females) for a year or so of training followed by decades of service in a reserve. The Baltic States have eliminated conscription and depend on fear (of the Russians) to obtain enough volunteers for their active-duty forces and much larger reserve. Beyond that all citizens are constantly reminded of how they can all resist an invader (Russia is the only likely one as the Germans, Poles and Swedes have abandoned imperial ambitions).
Initially Russia thought they could exploit the Russian minorities in the Baltic State. After independence in 1991 many nations formerly part of the Soviet Union found they had large Russian minorities that they had accumulated during years of “Russian occupation.” In many of those nations the Russians were not welcome and many went back to Russia. In the Baltic States, Belarus and Ukraine these Russian minorities noted the chaos in Russia and most adapted to their new homeland by learning the local language. This was difficult in Estonia, which was ethnically related to Finland and natives, like those in Hungary, spoke a distinct Central Asian language. Many Russians in Estonia, Finland and Hungary never bothered to do that when Russia was in charge. After 1991 most Russian speakers in these new nations realized learning this difficult language was worth the effort, and Russia found they could not rely on these Russian minorities to support Russian efforts during another attack and occupation. Russia tried to use this angle in Ukraine, but most of the Ukrainian Russians resisted and still do. This often meant leaving Russian occupied portions of Ukraine and later taking up arms to fight the 2022 invasion. A similar thing happened in Belarus, which prevented Russia from persuading Belarus to send troops in Ukraine. Worse, many Belarussians supported Ukraine and sabotaged the Russian war effort.
Before deciding to invade and annex all or portions of these former Soviet territories Russia, tried Cyber War against the more prosperous and affluent former Soviet territories. At the top of this list was Estonia, which was hit by a massive Russian Cyber War attack in 2007. The Estonians withstood the attack despite the temporary damage it did to their economy. This was something a NATO member had never faced before and Estonia pointed out that if there was no NATO response to the Russian attack on Estonia, the Russians would be tempted to try it on other new NATO members in East Europe.
This led to a 2010 agreement with NATO to facilitate cooperation between NATO and Estonia if Estonia is hit by another Internet based attack. In 2008, NATO established a Cyber Defense Center in Estonia. This, and the 2010 agreement, was a result of being called on by Estonia, in 2007, to declare Cyber War on Russia. That was because Russia was accused of causing great financial harm to Estonia via Cyber War attacks, and Estonia wanted this sort of thing declared terrorism, and dealt with. NATO agreed to discuss the issue, but never took any action against Russia. The new agreement creates a legal framework for striking back, or at least to defend Estonia more vigorously if there is another attack.
Most NATO members, especially the ones farther away from Russia, did not believe Russia would risk invading a NATO member. The attitude began to change in 2014 when Russia suddenly seized and annexed Crimea, which was part of Ukraine but contained many non-Ukrainians. Months later Russia tried to do the same to two provinces in eastern Ukraine called the Donbas, but that was only partially successful because of a prompt and unexpected Ukrainian response. Russia justified these actions to prevent Ukraine from joining NATO and the EU (European Union). The new NATO members pointed out Russia was not quitting and their military threat was going to escalate. The original NATO members were not convinced and thought Russia would be deterred by some economic sanctions. That was proved wrong in 2022 when Russia attempted to take all of Ukraine by force. Suddenly the fears of the new NATO members were recognized as prophetic rather than alarmist. The Baltic States prepared for war and former neutral nations Finland and Sweden, applied for NATO membership. Ukraine became an informal NATO member and received substantial military, economic and diplomatic support in their fight against Russia.