Hitler was extremely powerful in Germany, so the public would do or believe anything he said. This was important and was what Hitler had been looking for all along, so now he was completely in control as long as the foreign powers didn't’ find out his real ambitions.
Hitler had no problem hiding his ideas, as the whole world was distracted by the war. The foreign powers were far more concerned with Hitler's foreign policy than his racial policy.
Behind the advancing German army were Nazis from the SS called the Einzatzgruppen. This squad executed anyone they thought that they needed to. At first it was only the people who were politically against them, but soon Jews were included in the act. The local people were under Hitler's control and helped to seek out Jews to be executed, this would have been because they had been ‘brainwashed’ by Hitler, but also, continuing on the ancient hatred of Jews. At first the Nazis only executed the adult males,, but soon they realised that if they spared the lives of the children and women, then a generation of children would grow up with a hatred of the Nazis, and would be very powerful. This was important to the move forward in execution for the Nazis as this meant that far more people had to be dealt with, and the whole operation was proving to be very expensive.
The Nazi party couldn’t turn back now, but as it was expensive and slow, the Einsatzgruppen was becoming a problem. The Nazis finally decided that something had to change when they realised that it was having a massive psychological impact on the executioners. The Nazis experimented with different, more effective ways of executing the Jews. They came up with the idea of using gases to kill them, as it was less personal and more efficient, than shooting one bullet per head. They had been planning this method for a while, and had already killed a lot of people with it, in 1940-41.
On 20th of January 1942 a top secret meeting was called, in Wannsee. This was to work out how things were to work in the ‘final solution’. The meeting included important figures, like , Hitler, Himmler, and Reinhard Heydrich. Heydrich organised all the details to do with the death camps and transportation. At this point they decided that the ghettos should be closed and al the Jews should be moved to east Poland to be executed.
The discrimination of the Jews increased greatly between 1939-45. I couldn’t give one main reason for the increase in action against them as I think it was a combination of lots of factors that lead to change.