Further bio on Pius XII

The First Nuncio in Berlin
Several years after he was appointed Nuncio to Germany, and after completion of a concordat with Bavaria, the nunciature was moved to Berlin. June 23, 1920 and 1925 respectively. Many of Pacelli's Munich staff would stay with him for the rest of his life, including his advisor Robert Leiber and Sister Pascalina Lehnert — housekeeper, friend, and adviser to Pacelli for 41 years.
In Berlin, Pacelli was doyen or Dean of the Diplomatic Corps and active in diplomatic and many social activities. There he met notables like Albert Einstein, Adolf von Harnack, Gustav Stresemann, Clemens August Graf von Galen, and Konrad Cardinal von Preysing, the later two he elevated to cardinal in 1946. He worked with the German priest Ludwig Kaas, who was known for his expertise in Church-state relations and was politically active in the Centre Party.[23]. While in Germany, he enjoyed working as a pastor. He traveled to all regions, attended Katholikentag (national gatherings of the faithful), and delivered some 50 sermons and speeches to the German people. [24]

While in Berlin he met many notables and that must have had the effect of broadening his horizons and diplomatic education. His experience in foreign policy and diplomacy was extremely varied and he exercised and learned diplomatic discretion that stood him well later and understandably formed his motivation leading to the Concordat with Nazi Germany to protect and guarantee Church neutrality the only viable solution to the existence of the Church. He understood the Totalitarian beast better, I believe, than any in his generation and was a lonely voice after the ascent of Hitler amidst the silence of the Western Democracies in condemning anti semitism and racism and continued Pius XI's tradition of Mit brennender Sorge .The democracies well knew of the scourge and paganism of Nazism from the many denunciations the world heard on Vatican radio founded by Pius XI.

Negotiations with the Soviet Union (1925-1927)
In post-war Germany, Pacelli worked mainly on clarifying the relations between Church and State (see below). But in the absence of a papal nuncio in Moscow, Pacelli worked also on diplomatic arrangements between the Vatican and the Soviet Union. He negotiated food shipments for Russia, where the Church was persecuted. He met with Soviet representatives including Foreign Minister Georgi Chicherin, who rejected any kind of religious education, the ordination of priests and bishops, but offered agreements without the points vital to the Vatican. [25] “An enormously sophisticated conversation between two highly intelligent men like Pacelli and Chicherin, who seemed not to dislike each other”, wrote one participant.[26] Despite Vatican pessimism and a lack of visible progress, Pacelli continued the secret negotiations, until Pope Pius XI ordered them to be discontinued in 1927.

Pacelli supported the Weimar Coalition with Social Democrats and liberal parties. Although he had cordial relations with representatives of the Centre Party such as Marx and Kaas, he did not involve the Centre in his dealings with the German government.[28]
Pacelli supported German diplomatic activity aimed at rejection of punitive measures from victorious former enemies. He blocked French attempts for an ecclesiastical separation of the Saar region, supported the appointment of a papal administrator for Danzig and aided the reintegration of priests expelled from Poland.[29]. Pacelli was critical of German policy regarding financial reparations, which he considered unimaginative and lacking a sense of reality.[30] He regretted the return of William, German Crown Prince from exile as destabilizing. After repeated German acts of sabotage against the French occupation forces in the Ruhr valley in 1923, German media reported a conflict between Pacelli and the German authorities. The Vatican denounced these acts against the French in the Ruhr. [31]

When he returned to Rome in 1929, praise was heaped by Catholics and Protestants alike on Pacelli, who by now had become more popular than any German cardinal or bishop,[32] which he had largely excluded from his negotiations and dealings with the German government