How did fear of communism work to Germany’s advantage in the early 1930s?

Western European nations were terrified in the 1930s that communism would spread to their shores. Russia had only become communist in 1917, eighteen years before Hitler began pushing into what he called "German" territory. Eighteen years may seem a long time to a student, but to the average adult it is yesterday. The fear was real to the social elites, especially as a core goal of communism was to spread it worldwide. The communists had made pushes to take political power in Germany several times—in 1918 and later 1932—that almost succeeded. The idea of a central European country like Germany becoming communist was a horror to western elites, who liked their power and privilege.
Therefore, many of the powerful supported the idea of a strong Germany expanding its borders to provide a buffer zone between themselves and the feared communists. If Stalin struck and tried to invade the west, a heavily militarized and enlarged Germany with a strong dictator who hated communism would buy them time to prepare a counter attack. Therefore, they essentially turned a blind eye to what Hitler was doing in violating international law.
It wasn't until Hitler signed a pact with Stalin to divide Poland that the western powers became very alarmed and fearful for their own skins. It hadn't quite dawned on them that Hitler might turn on them. It was after Hitler invaded Poland in 1939 that the Allies declared war.

In the period right after World War I, Germany underwent a revolution in which many different parties were vying for control of the country, including the Communists. Many Communists were agitators from the Soviet Union as well as former German POWs who were radicalized while in detention. The period after World War I was quite turbulent for Germany. The Nazis were able to cash in on this by claiming that the Communists were one of the parties that sold out Germany and caused the humiliation of the Versailles Treaty. The Nazis were also able to use communism as a way to point out the Soviet Union as the number one ideological enemy of Germany. Since many Communists in the Soviet Union were also Jewish, the Nazis were able to link Communists and Jews as enemies of the German state. These became the two major scapegoats on which the Nazis were able to blame all of Germany's problems.