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On 21 September, the Soviets and Germans signed a formal agreement coordinating military movements in Poland, including the "purging" of saboteurs. A joint German–Soviet parade was held in Lvov and Brest-Litovsk, while the countries commanders met in the latter location. Stalin had decided in August that he was going to liquidate the Polish state, and a German–Soviet meeting in September addressed the future structure of the "Polish region". Soviet authorities immediately started a campaign of Sovietization of the newly acquired areas. The Soviets organized staged elections, the result of which was to become a legitimization of Soviet annexation of eastern Poland.

Where were cooperative military parades held?
Lvov and Brest-Litovsk