Polish officials have slammed a Berlin show commemorating Germans forced from eastern Europe after 1945 saying it attempted to rewrite history and could further strain relations between the two neighbours. The exhibition which opened on Thursday (August 11) shows the history of displacements in the 20th century and is organised by the Centre Against Expulsions. The centre is closely linked to the League of Expelled Germans representing 12.5 million Germans evicted from eastern parts of the defeated Third Reich after World War Two. Poland's conservative government and many Poles believe the organisation seeks to portray Germans as victims of a war they started. The Polish Ambassador for Trade and Culture in Berlin, Sawomir Tryc said the League's exhibition is dangerously one-sided. "Because they only show parts of Europe's history, or rather of European thought, then you loose sight of the causes, and that means that in this way they relativise the question of guilt, and it can lead to, it doesn't have to, but it can lead to a reversal of roles and mistaking the victims for perpetrators," Tryc said. "The acknowledgement of the border between Germany and Poland was the basis of German-Polish reconciliation, and whoever questions this basis, then it means that they are against German-Polish dialogue," he added.. The exhibition opened in central Berlin without major disturbance, although around 30-40 people gathered to protest outside the building housing it. Some opponents of the show held up banners emblazoned with Polish slogans, while others supporting the expelled Germans had posters demanding their own rights. In an address marking the opening, officials did not respond to Polish criticism and said the show was intended to commemorate all the victims of forced expulsion in Europe, not just German ones. "Whoever doesn't want to prolong the past into the future, they have to learn the lessons of history, as far as experience can be passed down from generation to generation, and impressions can be changed," said the President of the German Parliament and member of the ruling German Christian Democrat party (CDU), Norbert Lammert. The League of Expelled Germans led by Erika Steinbach, also a member of the CDU, hopes the show will pave the way for a permanent centre on that subject in Berlin, a project hotly contested in Poland. This idea has made Steinbach and the League hated figures for many Poles. A weekly has portrayed them in black SS uniforms. Poland's acting mayor of Warsaw has cancelled a trip to Berlin, saying he could not visit the city while the exhibition was running. Kazimierz Marcinkiewicz, who was due to travel to Berlin on Friday (August11) to celebrate the 15th anniversary of a partnership between the two cities, said that after the opening of the show he decided to change his plans. Marcinkiewicz, who served as prime minister in the conservative government until last month, told Polish private television TVN 24 late on Thursday, that his visit could be misinterpreted and abused under the circumstances. Polish Prime Minister Jaroslaw Kaczynski has also condemned the show as a worrying and sad event, and the foreign ministry issued a statement on Friday saying the show could further strain relations between the two neighbours. Nazi Germany invaded Poland in September 1939 after a secret pact between Adolf Hitler and Soviet leader Josef Stalin to partition the country. After Germany's defeat, Poland's borders were shifted west and many Germans were forced to flee. Thousands died on the trek from Poland, Hungary and what was then Czechoslovakia. At the same time, Poles from the east of the country were uprooted from land which became part of the Soviet Union. Germany's government is cautious about the idea of creating an Centre for the Expelled in Berlin, but Poles are irritated it has not rejected the plan outright. Relations between the two countries, now European Union partners, warmed after the fall of communism, but soured when plans for the Centre were first announced and some Germans signalled they would seek compensation for lost homes and land. Poland also felt snubbed over a planned German-Russian gas pipeline by-passing its territory and relations deteriorated further this year when left-wing German daily called President Lech Kaczynski and his twin brother Jaroslaw "potatoes."