The Nazis used the killing of a German diplomat in Paris by a young Polish Jew, Herschel Grynszpan, as an excuse. Over two nights SA stormtroopers and civilians burned hundreds of synagogues and smashed the windows of thousands of Jewish shops, while police and firemen stood by.
At least 91 Jews were murdered and about 30,000 Jewish men were sent to concentration camps. Many historians see the night as a turning point on the road to the Holocaust.
Source: Wikipedia