The train was trundling through the Warsaw suburbs towards the north-west. It was Easter weekend, and many travellers were on their way to family gatherings in the provinces. I shared the carriage with an elegantly dressed young Polish woman, who had studied in Birmingham and spoke fluent English. She now worked in Warsaw as a translator of Polish films. When I mentioned to her that in 2018 Poland would celebrate the centenary of its independence, she smiled hesitantly and said: “Yes … maybe we will get there.”

Nothing paints as poignant a picture of Europe’s history as a journey across this country, whose borders have shifted so many times and lands have been carved up so ruthlessly that it nearly disappeared from the map. It was a key battleground for two world wars, the scene of horrendous crimes, then became trapped for four decades behind the iron curtain. Today, Poland is the continent’s economic growth champion, a genuine success story of post-communist transition. But understandably, it is not free of anxieties.

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Russia’s aggression against neighbouring Ukraine has changed almost everything. Poland is deeply concerned about its national security and about the degree of solidarity its western allies are able – and willing – to demonstrate. This anxiety is not limited to the ruling class, or politicians. It is deeply felt by the population. On 10 April, Poland will commemorate the fifth anniversary of the plane crash in Smolensk that killed its then president and 95 other Poles, many of whom belonged to the military and defence elite – a traumatic episode that was made worse by Russia’s refusal to authorise the return of the wreckage. All this explains why the woman on the train made nervous jokes about Poland making it to that anniversary unscathed.

From afar – from London, Paris or Berlin – there is still a tendency to see Poland as something of a backwater, a place of rich culture but essentially an economic hinterland for Germany’s powerful industry, a country of low salaries whose youth stream out in search of better paid jobs (2.2 million Poles live in other EU countries, some 600,000 of them in the UK). One hears western officials comment off the record that the Poles, along with the Baltic people, are a bit paranoid about Russian aggression and too obsessed with their historic grievances. It’s crazy to think Vladimir Putin would attack Poland, say these westerners.

But Poland got one thing right: it never believed in “the end of history”, Francis Fukuyama’s 1989 formula proclaiming the inevitable triumph of liberal democracy over ideology. This scepticism led Poland to push extremely hard for admittance to Nato and the EU, both seen as virtual life insurance policies for the nation. The profound transformation Poland has undergone, sometimes through painful shock therapy, has not only been a matter of improving living standards, but comes from a desire to cement its national security. In 1989, its GDP per capita was around 5% of the western European average. Today it’s 70%.

Nato has tried to send reassuring signals, for example by, for the first time, conducting military exercises in Poland

“Poland is a fundamentally vulnerable country because it has no natural barriers against more powerful countries in the east and west, which was a curse in our history,” says former foreign minister Radek Sikorski. Now president of the Polish parliament, he describes the profound shifts that have occured in his country as follows: “In 1989, all of our neighbours changed, and we found ourselves with benign neighbours”. Russia withdrew its troops and didn’t oppose Poland’s integration with the west. Germany became a friend. In the last 25 years, we have used this historical window rather well – to modernise, integrate with the west and build a new society. But this was predicated on international circumstances that are now being challenged by the first forceful changing of borders on the European continent since the second world war.”

Nato has tried to send reassuring signals, for example by, for the first time, conducting military exercises in Poland, or by making plans for a new “rapid reaction” force. A column of American troops recently travelled across Poland in a show of solidarity. But doubts remain whether article 5 of the North Atlantic treaty, the “all for one, one for all” security guarantee the alliance provides, is sufficient to discourage Putin from more war-mongering.

Poland would much prefer to have two US brigades under Nato command stationed on its territory. This was opposed by Germany on the grounds that it would violate the Nato-Russia agreement of 1997. Polish officials have a point when they say privately that the German position is questionable, because the agreement explicitly rested on the notion that strategic circumstances would remain unchanged in Europe, which is no longer the case. A Polish diplomat put it to me this way: “In 2014, with the Russian annexation of Crimea and the Russian assault in the Donbass, the unthinkable became reality.”

Poland was equally irritated about being left out of the Franco-German efforts to negotiate a ceasefire between Russia and Ukraine. It saw that as another German concession to Putin. Events in Ukraine are closely watched by Warsaw, as a test of Europe’s capacity to defend its principles and interests. “If Putin is undeterred in Ukraine, he may go further and stir trouble, for example in the Baltic states. If he is not met with a sufficient response, it will open an era of Nato weakness that would be very undermining,” says Marcin Zaborowski, who heads the Polish Institute of International Affairs.

Poland intends to spend €40bn on a missile defence system, attack helicopters, submarines, armed vehicles and drones

Polish anxiety is only enhanced by the feeling that, as Zaborowski puts it, “we are lonely in the region”. The Baltic states may share Poland’s perspective. But Hungary is seen as a client-state of Russia, and the Czech Republic and Slovakia have failed to put brakes on the penetration of Russian capital and influence, which is felt in their criticism of European sanctions against Russia. Central Europe has become geopolitically fragmented.

So how is Poland reacting to all this? First, it is planning to modernise its armed forces. It intends to spend a whopping €40 billion over the next 10 years on a missile defence system, attack helicopters, submarines, armed vehicles and drones. American, French and German defence industries are all lining up to compete. Whether Poland chooses to buy European or American equipment will be an indicator of where it believes its best security guarantees lie, and also of what hopes remain for a common European defence policy.

Second, Poland is pushing for maximum western solidarity towards Ukraine, hoping for the equivalent of a Marshall plan. If Ukraine manages to save itself from economic collapse, Poland will feel safer.

Third, Poland wants to revive the diplomatic alliance of the “Weimar triangle” (comprising France, Germany and Poland), whose foreign ministers recently met in the western Polish city of Wrocław. The feeling in Warsaw is that even if the German chancellor Angela Merkel rightly has no illusions about Putin, Germany has tended to monopolise European foreign policy in dealing with Russia.

Before she got off the train, my young Polish travel companion said that after war broke out in Ukraine, her family discussed emigrating to New Zealand. “You see,” she explained, “we agreed that if the worst were to happen, we weren’t the type of people who would take up arms. Other Poles would though.” I realised what a huge gap remains between my western European mindset and that of central Europeans. History can change much more quickly here.

• This article was amended on 10 April 2015 to correct the name Zaborowski and placename Wrocław, which were misspelt as Zaborowki and Wroclaw.