One reason Adolf Hitler believed war was necessary.

One reason Adolf Hitler believed war was necessary was due to his ideological belief in Lebensraum, which in German means "living space." Hitler and his followers in the Nazi Party advocated for the expansion of Germany to provide the allegedly superior "Aryan" race with adequate room to live, grow, and prosper. He argued that the current territory of Germany was insufficient to sustain its population and economy in the long run. Hitler claimed that the acquisition of new territories, particularly in Eastern Europe, would provide the necessary resources and space for the German people. This expansionist policy was a central tenet of his foreign policy and a pretext for the outbreak of World War II when Nazi Germany invaded Poland in 1939, seeking to annex territory for living space.

The concept of Lebensraum was not only a tactical policy but also deeply embedded in Hitler's worldview, which was characterized by social Darwinism. He perceived history as a struggle between races for survival and domination, and he considered Slavic peoples, particularly Poles and Russians, as well as other groups, to be inferior. He believed that these territories were destined to be governed by the superior Germans. The pursuit of Lebensraum was thus tied to a genocidal policy against those seen as standing in the way of German expansion, leading to immense suffering and loss of life. This ideological stance was partly a continuation of a broader German nationalist thought dating back to the 19th century and was detailed in Hitler's book, "Mein Kampf" (My Struggle), which became a fundamental text of Nazi ideology. The pursuit of Lebensraum and other aggressive policies pursued by the Nazis would ultimately lead Europe and much of the world into the devastating conflict of World War II.