In 1797 Jan Henryk Dąbrowski turned to general Napoleon Bonaparte during his campaigne war in Italy, with the proposal to create Polish wards at his side. Napoleon liked the idea of establishing Legions with Poles. Legionnaires took part in the Italian campaign. Unfortunately after that  unnecessary Polish legionnaires were sent by Bonaparte with French army to the island San Domingo to suppress the uprising of the black population against French domination there. Only few came back to Europe.

When Napoleon fought against Prussia and Austria, wanting to recruit the essential support and soldiers, became interested again in the Polish issue. However he made no promises of the reconstruction of the Polish state.

In 1806 in Westpoland an uprising against Prussia broke out. It facilitated French army reaching Polish land. Armies Napoleon was enthusiastically welcomed at December 1806 in Warsaw, left by Prussians. · in 1807 Napoleon Bonaparte created Duchy of Warsaw and granted it the Constitution, based on the Code of Napoleon .  In the campaign against Russia in 1812, the Polish army stood at the side of Napoleon.

100 thousand Polish soldiers under the prince's of Józef Poniatowski command  fought in the battle of Smolensk, Borodino, they reached Moscow along with the Great Army and shielded the reverse of Napoleon during the crossing through Berezynę. In the Russian campaign 70 thousand Polish soldiers died.

Defeat of Napoleon in so-called,, battle of nations "in 1813 and Waterloo in 1815 was the end of not only the Polish army, but also of the existence of the Duchy of Warsaw.  Victorious powers during the congress in Vienna decided of its future.