In mid-1916, after the Battle of Kostiuchnówka (4–6 July 1916), in which the Polish Legions delayed a Russian offensive at a cost of over 2,000 casualties, Piłsudski demanded for the Central Powers to issue a guarantee of independence for Poland. He backed that demand with his own proffered resignation and that of many of the Legions' officers. On 5 November 1916 the Central Powers proclaimed the "independence" of Poland, hoping to increase the number of Polish troops that could be sent to the Eastern Front against Russia, thereby relieving German forces to bolster the Western Front.