Was the desire to kill Jews a primary cause of WWII?
The Nazi Party had an obvious goal to commit extensive murders against the Jewish population years prior to World War II .Was this the primary cause for the start of the war?
No. Absolutely not. The killing of Jews was not the main reason for the starting of the war. Instead, the Nazis were interested in starting the war because they wanted to recoup losses from WWI and they wanted (ultimately) to get more "living room" in the East. They did not set out to take over Poland and parts of the Soviet Union for the purpose of killing the Jews who lived there.
The main cause of the war was the fact that Germany had been hurt by the Treaty of Versailles after WWII. They felt that they had had territory unfairly taken away and they did not like the fact that German-inhabited areas had been given to other countries. They wanted to get these places back and they ultimately wanted to conquer some areas in Eastern Europe so as to expand the land area available to them. Neither of these goals had anything to do with the Jews.
No, the primary cause of WWII's Allied response to Hitler's Germany was the other countries concerns about their borders and sovereignty. The aftermath of the First World War had not left Europe as an entirely stable region.
Although there were humanitarian concerns in WWII, they were not enough to cause the Allied nations to directly confront the Axis. In fact, the practice of appeasement, or letting Germany take over small neighboring countries, was used until it became clear that Hitler would not, in fact, be appeased by these smaller gains. See attached article.