Berlin is the capital city of Germany. While not directly visited or mentioned in the original seven novels, its historical context is highly significant to the global wizarding war waged by Gellert Grindelwald. Albus Dumbledore's legendary duel and defeat of Grindelwald occurred in 1945, the same year as the end of the Muggle's Second World War, in which Berlin was a key city. This timing suggests that Grindelwald's European power base was analogous to the Axis powers, with Germany as a central theatre of his operations. Supplementary materials confirm Berlin's importance in the wizarding world. The German Ministry of Magic is located within the city (Pottermore). In the early 1930s, Berlin served as the venue for the election of the new Supreme Mugwump of the International Confederation of Wizards. The event was a focal point for Gellert Grindelwald's attempt to gain legitimate political power, which he sought to manipulate by using a charmed Qilin (Fantastic Beasts: The Secrets of Dumbledore).
In the primary book series, Berlin's role is implied rather than stated. It serves as a historical backdrop for the rise and fall of Gellert Grindelwald, a dark wizard whose reign of terror across continental Europe concluded with his defeat in 1945. This event, which ended a global-scale wizarding war, is a major part of Albus Dumbledore's personal history and established his reputation as the most powerful wizard of his time, with the exception of Lord Voldemort. In the wider wizarding world narrative, Berlin is the setting for a crucial confrontation. During the Supreme Mugwump election, Newt Scamander and his allies worked to expose Grindelwald's plot. They successfully revealed that Grindelwald's chosen Qilin was enchanted and presented the true Qilin, which subsequently bowed to Vicência Santos, leading to her legitimate victory. This event thwarted Grindelwald's plan for a bloodless takeover of the wizarding world and forced him to flee, escalating the conflict (Fantastic Beasts: The Secrets of Dumbledore).
J.K. Rowling deliberately set the year of Grindelwald's defeat as 1945 to create a direct parallel with the end of World War II. This historical resonance strongly implies a connection between Grindelwald's regime and Nazi Germany. The Fantastic Beasts film series made this connection explicit by setting a significant portion of The Secrets of Dumbledore in 1930s Berlin, directly involving the German Ministry of Magic in the political struggle against the rising dark wizard.