It's really, really complicated, but here's a basic timeline. Some good readings would be Black Earth by Timothy Snyder, Origins of the Final Solution by Christopher Browning, and War and Genocide by Doris Bergen. The biggest shift in laws were the Nuremberg Laws of 1935 which stripped Jews in Germany of their citizenship. Mass violence began on Nov. 9, 1938 with the Kristallnacht Pogrom. Between 1933 and 1939 the Germans focused on attempting to push Jews out of the country through forced emigration and making life unlivable in Germany. At the same time they enacted policies which made it harder for German Jews to escape, and the rest of the world closed its borders. It is important to note that he Nazis could not have carried out the Holocaust without the war, at least not on the scale they did because relatively few Jews lived in Germany, and many thousands left during the 1930s. Germany had a couple hundred thousand Jews, in Poland alone there were over 3 million Jewish people. Half of the six million Jews killed in the Holocaust were Polish, making the death rate for Polish Jews upwards of 90%. Although Germany had hundreds of concentration camps as early as 1933, for the most part these camps were not where the Holocaust happened, at least not by numbers. These camps were horrific, but they were for the most part places where people were imprisoned over a period of time, they were tortured, starved, and many were killed. Death camps on the other hand were places where most people were murdered within hours or days of arrival. The Holocaust happened where Jews lived in massive numbers, so it happened in the areas of Eastern Europe occupied by the Nazis. Jews from Germany and other parts of Western Europe were by enlarge transported to the East to be killed. The period of mass, genocidal killing began somewhere between 1940 and 1941, and amped up significantly when the Nazis invaded the Soviet Union in June 1941. When the Nazis invaded the USSR they did so with various murder squads, the Einsatzgruppen and others, including Wehrmacht soldiers and locals who went through towns carrying out mass shootings of Jews. These killings had anywhere from a few dozen victims a day, to in the case of the Babi Yar massacre, over 30,000 in a period of a few days. Later, gas vans began to be used. The Nazis had been in power for over 7 years when gas chambers and the infamous Zyklon-B were first used to kill mass numbers of Jews. And though the mass murder took a while to get going, once it started it happened very quickly. Take the Lithuanian example. The Nazis invaded in June 1941, and by the time the US entered the war on Dec. 7, 1941, 85% of Lithuanian Jews had been murdered. Scholars generally accept four stages of the Holocaust which fit inside Gregory Stanton's 8 Stages of Genocide. These steps are identification, separation, concentration, and extermination. These steps could take anywhere from years, to a few days. First, in every area they occupied the Nazis identified the Jews in some way, either by registration, wearing of the yellow star or star arm band, or by adding identifying marks to documents like passports or identification cards. They then enacted policies to separate Jews from the rest of the population, mostly this was done by removing them forcefully from communal areas like schools, the economic structure, and the workforce. They were then concentrated in places like ghettos, or else in staging grounds where they would then be moved somewhere. That somewhere were extermination centers in the East where they were killed by shooting or gassing.