Germany lost world war i and experienced severe problems with economic recession, unemployment, and horrific inflation during the 1920s. which theory/theories best explains the rise of the nazi party in germany in the 1930s?

"It's the economy, stupid."  That was the campaign slogan of an American presidential campaign some years ago.  The challenger was able to defeat a previously popular president because the economy had taken a downturn. Governmental leaders often are blamed for bad economic conditions and people will listen to other potential leaders who make strong promises about better economic hopes.  Assuredly, that happened in Germany during the days of the struggling Weimar Republic government, when the loud promises of Hitler and the Nazis brought them to power.

There's a name for the theory of blaming someone for bad conditions -- even if those persons aren't directly responsible for the bad conditions.  It's called   scapegoat theory.  The image of the "scapegoat" comes from an Old Testament ritual in Israel.  A priest pronounced the sins of the nation onto a goat, and then that goat was chased out into the desert never to be seen again.  Blaming the Weimar Republic leaders for the bad economic conditions was a sort of scapegoating.  Given the harsh terms faced by Germany in the treaty after they lost World War I, there was little hope of Germany's economy recovering.  

An even more glaring example of scapegoat theory also was practiced by the Hitler and the Nazis.  Hitler was fiercely anti-Semitic -- against the Jewish people.  His rhetoric and the Nazi agenda blamed the Jews for Germany's loss in World War I and for Germany's bad conditions.  The Jewish people in Germany became a hated scapegoat and Jews were persecuted severely once the Nazi party came into power.

The answer is installation.