Shortly before 5am on 1 September 1939, the German battleship Schleswig-Holstein fired at a garrison of Polish soldiers stationed on the Westerplatte peninsula, part of what was then the internationally administered city of Danzig, now Polish Gdańsk. The attack marked the start of a war that would eventually kill millions and go down as the most appalling conflict in the history of humanity.

As the 80th anniversary of the outbreak of the second world war approaches on Sunday and European leaders head to Poland for commemorations, the bloody events of 80 years ago are being politicised and exploited more than ever across the continent.

The Schleswig-Holstein bombards the ammunition dump on the Westerplatte on 1 September 1939. Photograph: Dpa Picture Alliance/Alamy Stock Photo

Poland’s nationalist Law and Justice (PiS) ruling party had invited Donald Trump to Warsaw to give the keynote speech at Sunday’s anniversary event, a move that many feared would hardly contribute to a tone of solemn commemoration. On Trump’s last visit to Warsaw, he invoked the war to speak of the west’s need to stand up to enemies, using dark, clash-of-civilisations rhetoric.

Trump’s last-minute decision to cancel his trip and send the vice-president, Mike Pence, in his stead, along with German chancellor Angela Merkel’s last-minute decision to attend, means there is less potential for grandstanding speeches on Sunday. But in Poland and across Europe, a bitter debate continues to rage on what lessons to draw from the second world war.

Ten years ago, on the 70th anniversary, the Russian president, Vladimir Putin, and Merkel met at Westerplatte, and there were signs that European nations may be edging closer to reconciliation over the terrible events of the war. As the new anniversary comes around, this time the atmosphere is very different.

In many central European countries, governments are focusing on Nazi atrocities during the war and playing down stories of local Holocaust collaboration, while nativist politicians across the region indulge in airbrushed, heroic war histories. In Britain, the war effort and casualties are regularly invoked in discussions about Brexit, leaving the outgoing German ambassador to suggest that the obsession with Britain fighting the Nazis does little to solve the problems of today.

In Russia, Putin has gradually transformed the war victory and the enormous Soviet sacrifice in the war into a bombastic celebration and a chance for militaristic posturing. In eastern Ukraine, Russian-backed forces have gone into battle carrying flags inspired by the second world war victory.

In the run-up to the anniversary, the Russian government launched a campaign to rehabilitate the Molotov-Ribbentrop pact, signed between Nazi Germany and the Soviet Union a week before the attack on Westerplatte, which included secret protocols by which the two powers would divide eastern Europe. Within a few weeks, Poland had been split and dismembered by the two powers.

Ten years ago, Putin used his speech at Westerplatte to say the pact was “from a moral point of view unacceptable and from a practical point of view pointless, harmful and dangerous”. He did not apologise, but called the agreement a “mistake”.

This year, the rhetoric from Moscow has been very different, as the foreign ministry launched an online campaign with slick animations and a #TruthaboutWWII Twitter hashtag. The culture minister, Vladimir Medinsky, wrote a column calling the pact “a triumph of Soviet diplomacy”. While Merkel and German president Frank-Walter Steinmeier will attend Sunday’s anniversary, Putin has not been invited.

Inside Poland too, the battles over war memory have grown more fierce. Until recently, the Westerplatte site, dominated by a communist-era granite monument, was controlled by the Gdańsk city administration, run by the liberal opposition to PiS. Recently, however, the central government has wrested control of the site through a court ruling, and wants to build a new museum to commemorate the heroism of the defenders, due to be built by 2023.

“I worry it will become a kind of historical Disneyland,” said Paweł Machcewicz, a historian who was the director of Gdańsk’s Museum of the Second World War until he was fired in 2017, shortly after it opened, after a media campaign that painted the museum as not patriotic enough and even “anti-Polish”.

His successor at the museum, Karol Nawrocki, who is in charge of planning the new Westerplatte site, made several changes to the exhibits of the main museum in Gdańsk. At the entrance to a hall featuring hundreds of photographs of Jews murdered in the Holocaust, the new curators inserted a wall-sized photograph of a Polish family executed for hiding Jews, something Machcewicz said he found a “totally inappropriate” addition to a room about the culmination of the Holocaust.

A display showing the number of deaths in each country was also amended to give deaths by percentage of civilian population, in order to show that Poland proportionately suffered more than others. About one in five Polish citizens were killed during the war.

Nawrocki, the government-appointed director who replaced Machcewicz, said the original museum had left out many “unquestionable Polish heroes” and said the focus on Polish heroism was unsurprising. “It was only in the 1990s that we had the opportunity to talk truly and objectively about Polish history. After 50 years of two totalitarianisms we should be allowed to talk about our own history,” he said. A court case has been brought by Machcewicz against Nawrocki and the museum.

Perhaps the biggest change at the museum was that of the final message given to visitors at the end of their visit. Previously, a four-minute video traced history since the end of the second world war and ended with images of wars in Ukraine and Syria and the refugees they created. This was replaced by a computer-generated video of stylised, heroic Polish soldiers in combat, changing the message from one of reflection on the horrors of war to one of patriotic glory.

Gdańsk’s liberal mayor, Aleksandra Dulkiewicz, who took up the post after the former mayor Paweł Adamowicz was stabbed to death earlier this year, said government messaging over the war was wrong-headed and inflammatory. City authorities plan their own, separate commemoration event on Sunday, where guests will include the mayor of London, Sadiq Khan.

“Of course Polish soldiers were heroes, but on the 80th anniversary this should not be the most important message. The other way to show this history is to think how tragic it was, and use it to create a new peaceful way of success for Poland,” said Dulkiewicz.