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How was Upper Silesia divided between Germany and Poland?

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Treaty of Versailles The “Big Four” (left to right): David Lloyd George of Britain, Vittorio Orlando of Italy, Georges Clemenceau of France, and Woodrow Wilson of the United States, the principal architects of the Treaty of Versailles.

Following the Treaty of Versailles, the division of Upper Silesia was determined by a plebiscite held on March 20, 1921, to decide whether the region should belong to Germany or Poland. Although more communes and a higher total number of votes favored Germany, the southeastern area—which was economically vital—showed strong support for Poland.12

Following a third Polish uprising in May 1921 and subsequent deliberation by the League of Nations, the Allied powers reached a compromise on October 20, 1921. While Germany retained the majority of the territory and population, Poland was awarded the southeastern portion of Upper Silesia. This area comprised approximately 1,300 square miles and included roughly one million inhabitants. Crucially, this partition granted Poland control over nearly three-quarters of the region's coal production and two-thirds of its steelworks, providing the new Polish state with a significant industrial foundation.12