Kościuszko did not believe that Napoleon would restore Poland in any durable form. When Napoleon's forces approached the borders of Poland, Kościuszko wrote him a letter, demanding guarantees of parliamentary democracy and substantial national borders, which Napoleon ignored. Kościuszko concluded that Napoleon had created the Duchy of Warsaw in 1807 only as an expedient, not because he supported Polish sovereignty. Consequently, Kościuszko did not move to the Duchy of Warsaw or join the new Army of the Duchy, allied with Napoleon.