According to Mein Kampf (My Struggle), Adolf Hitler first began to develop his views through observations he made while living in Austria. He concluded that there was a racial, religious, and cultural hierarchy, and he placed "Aryans" at the top as the superior race and Jews, "Gypsies" (the Roma) and Slavic people at the bottom. He closely examined and questioned the policies of the Austro-Hungarian Empire, where as a citizen by birth, Hitler lived during the Empire's last throes of life. He believed that its ethnic and linguistic diversity had weakened the Empire and helped to create dissention. Further, he saw democracy as a destabilizing force because it placed power in the hands of ethnic minorities who, he claimed, "weakened and destabilized" the Empire by dividing it against itself.
Nazi thought, an extension of various philosophies, came together at a critical time for Germany; The nation had just lost World War I and was in the midst of a period of great economic depression and instability. The Dolchstosslegende, which held that the war effort was sabotaged internally, brought to question the extent of profiteering and the supposed "lack of patriotism" displayed during the war. In the realm of politics, these charges were directed towards the Social Democrats and the Weimar government, as the latter had been accused of "selling out" the country. Additionally, the Dolchstosslegende encouraged many to look at "non-German" Germans critically, especially those with potential "extra-national loyalties", such as the Jews. Such an appeal capitalized on anti-Semitic sentiments.
Nazi rationale also invested heavily in the militarist belief that great nations grow from military power and maintained order, which in turn grow "naturally" from "rational, civilized cultures". The Nazi Party appealed to German nationalists and national pride, capitalizing on irredentist and revanchist sentiments as well as aversions to various aspects of modernist thinking. Many ethnic Germans still had heartfelt ties to the goal of creating a greater Germany and some felt that the use of military force was necessary to achieve it.
http://en.wikipedia.org/wiki/Nazism