The Storm Troopers, or Sturmabteilung (SA), were a paramilitary organisation within the Nazi Party in interwar Germany, founded to protect Nazi meetings from disruption and to break up the meetings of other parties; they were also used to intimidate, beat up and murder Jews and opponents of the Nazis and to create a climate of fear on the streets of Germany. They were commonly referred to as "brownshirts", in reference to the color of their uniforms.
The SA was a major participant in the Kristallnacht ('Crystal Night' or 'Night of the Broken Glass') pogrom of 9-10 November 1938, in which an estimated number of between 91 and 200 Jews were killed and thousands more sent to concentration camps (of whom a large number were later murdered). Some 7000 Jewish shops were looted and more than a thousand synagogues destroyed.
It was led by Ernst Röhm, who had been a co-founder of the paramilitary organisation. During the early 1930s Röhm's SA ("brownshirts"), with 2.9 million members, was a much larger and more powerful part of the Nazi Party than Heinrich Himmler's SS. That suddenly changed in June 1934 as a result of a power struggle between the SA, which had a more radical vision than Hitler would tolerate, and a coalition of Himmler, Hermann Göring, the army and big business. The army feared the SA would absorb it into its ranks; which is what Röhm wanted to do. Himmler and Reinhard Heydrich prepared the list of Röhm's SA associates who were executed or imprisoned in the "Night of the Long Knives" which took place between June 30 and July 2, 1934. Hitler had Röhm killed as well, for fear that he would be a rival in the near future. Himmler and his SS gained enormously from the killings; the SS became its own branch and Himmler reported only to Hitler.
The term is sometimes erroneously broadened to include all Nazis and even all fascists, although strictly speaking Italian fascists were Blackshirts, for similar reasons of their uniform.  The term was also used in World War I to denote special trench assault units of the German Army.