From the 10th century onward, the Piast-ruled Kingdom of Poland established under Duke Mieszko I had close and chequered relations with the Holy Roman Empire.

From 1945–1950, a series of flights and expulsions occurred, in which up to 11 million ethnic Germans were forced to leave their homes in Poland and resettle in post-war West and East Germany.

As he could not prevail against Gero, Mieszko I resorted to consolidate his realm: he strengthened the relations with the Bohemian duke Boleslaus I by marrying his daughter Dobrawa and converted to Christianity in 966.

Meanwhile, Poland had to face the claims to universal power raised by Otto I when he had conquered the Kingdom of Italy and was crowned Holy Roman Emperor by Pope John XII in 962.

According to the idea of the translatio imperii, the Emperor would continue the tradition of the Roman and Carolingian Empire as guardian of the Catholic Church superior to all secular and ecclesiastical rulers.

Mieszko sought to improve the relations with Otto I: he appeared as amicus imperatoris at the Imperial Diet of Quedlinburg in 973 and in 978 secondly married Oda, the daughter of Dietrich of Haldensleben, margrave of the Northern March.

He timely switched sides, when he realized that Otto's mother Theophanu would gain the upper hand and in turn sparked a long-term conflict with the Bohemian dukes over Silesia and Lesser Poland.

Mieszko backed the German forces several times against the revolting Lutici (Veleti) tribes (though to no avail) and until his death in 992 remained a loyal supporter of the Emperor.

Throughout the Middle Ages, the Germans expanded eastwards from modern western and central Germany into the less populated regions, east of Elbe and Saale rivers, which were inhabited by Baltic, Finnic and Slavic peoples, including Poles.

Bernhard von Bülow, who served as Chancellor of Germany from 1900 to 1909, called the Polish victory over the Teutonic Knights at the Battle of Grunwald in 1410 the Germans' most portentous national disaster.

Its founder and principal ideologue Roman Dmowski even claimed the industrialized Prussian east as the bedrock of the Polish nation to regain independence.

[citation needed] Following the Oath crisis, in July 1917, the Germans arrested Józef Piłsudski and his close associate Kazimierz Sosnkowski and then imprisoned them in Magdeburg.

Already in 1922, Chief of the German Army Hans von Seeckt stated: Poland's existence is intolerable and incompatible with the essential conditions of Germany's life.

[29] Germany carried out mass arrests, expulsions, deportations to concentration camps and assassinations of local Polish leaders, activists and prominent individuals.

On 31 August 1939, Germany staged the Gleiwitz incident, a false flag attack which was to serve as a casus belli to justify the invasion of Poland, which started the next morning,[31] without a declaration of war.

[35][36] Polish slave workers were obliged to wear "P" badges and were subjected to strict segregation policies, with certain activities, such as sexual intercourse with German people, being punishable by deportation to concentration camps or death.

During the latter, SS chief Heinrich Himmler anticipated a total destruction of Warsaw, the capital of the former Polish nation, which has supposedly blocked the Germans' road to the east for 700 years.

[43] During the Cold War, East Germany shared the fate of Poland, which fell into the Soviet sphere of influence, and both countries had Soviet-installed communist regimes, and therefore enjoyed good relations.

However, while the Poles were still insisting 20 years after the end of the war that the 1945 Potsdam Agreement had created favorable and just borders encompassing the entire historical territory of Poland, the GDR saw the loss of the old German East as a reparation for the Nazi crimes against the Polish nation.

The European policy of détente at the beginning of the 1970s, and in particular the signing of the Warsaw Treaty ushered in the next phase of family reunions and departures of Germans, preferably the "autochthonous" population, from Poland, especially to West Germany.

The Warschauer Kniefall gesture by Chancellor and future Nobel Peace Prize laureate Willy Brandt, which took place at the Monument to the Warsaw Ghetto Uprising Heroes in 1970, was regarded as a major step in the process of reconciliation between the two countries.

Due to large anti-communist protests and the emergence of the Solidarity movement in Poland, East Germany unilaterally terminated the visa-free travel agreement and closed the border.

[citation needed] After the fall of communism, Poland and the reunited Germany have had a somewhat positive, but occasionally strained relationship due to sensitive political issues.

In March 1990, German chancellor Helmut Kohl caused a diplomatic firestorm when he suggested that a reunified Germany would not accept the Oder–Neisse line, and implied that the Federal Republic might wish to restore the frontier of 1937, by force if necessary.

[51] Earlier in December 2021, German Chancellor Olaf Scholz rejected the idea of paying further World War II reparations to Poland.

[57][58] However, as a consequence of the Potsdam Agreement, Poland obtained a quarter of originally Polish but Germanized territory in the borders of 1937 whose largely German-speaking population which was subjected to expulsion and Polonization.

[65] German–Polish relations are sometimes strained when topics like World War II and the postwar forced expulsion of the German citizens from the territories assigned to Poland are brought up.

In 2018, Polish Foreign Minister Jacek Czaputowicz and his German counterpart Heiko Maas agreed a to pass a declaration specifying the strategic priorities for German-Polish cooperation which stated that "both countries support a multilateral, rules-based order and champion a united Europe".

[77] On 15 September 2021, the German Foreign Minister Heiko Maas announced a project to build a monument commemorating the Polish civilian victims of World War II in Berlin that would "honour their lives, their resistance and their courage".

Prime Minister Donald Tusk and Chancellor Olaf Scholz stressed the close relationship between the two countries and announced a joint action plan for a more intense cooperation between Poland and Germany in key areas including security and defence, support for Ukraine in the context of the ongoing Russian invasion, business relations, enlargement of the EU and questions regarding history.