German troops invaded Poland on September 1, 1939, triggering World War II. To justify the action, Nazi propagandists accused Poland of persecuting ethnic Germans living in Poland. They also falsely claimed that Poland was planning, with its allies Great Britain and France, to encircle and dismember Germany. Poland mobilized late, and political considerations forced its army into a disadvantageous deployment. The Polish army also lacked modern arms and equipment, had few armored and motorized units, and could deploy little more than 300 planes, most of which the Luftwaffe destroyed in the first few days of the invasion. Despite fighting tenaciously and inflicting serious casualties on the Germans, the Polish army was defeated within weeks.In response to German aggression, Great Britain and France declared war on Nazi Germany.