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In page Poznań:

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In the Greater Poland uprising of 1806, Polish soldiers and civilian volunteers assisted the efforts of Napoleon by driving out Prussian forces from the region. The city became a part of the Duchy of Warsaw in 1807, and was the seat of Poznań Department – a unit of administrative division and local government. However, in 1815, following the Congress of Vienna, the region was returned to Prussia, and Poznań became the capital of the semi-autonomous Grand Duchy of Posen. Around 1820, Poznań had over 20,000 inhabitants, 70% of whom were Poles, 20% Jews, and 10% Germans.[citation needed]