Alfred Rosenberg was an early member and leader of the Nazi party who developed many of their racist ideals. He published articles promoting the conquest of Eastern Europe and was later executed as a war criminal. The SS began as Hitler's personal bodyguards but grew drastically under Himmler to become one of the largest groups in Nazi Germany. They remained fiercely loyal to Hitler and guarded key Nazi meetings and facilities. The Nazi concept of Lebensraum called for expanding German territory eastward to settle ethnic Germans and remove Jews, Slavs, and others deemed inferior to make room for the German "master race." This idea was outlined in Hitler's Mein Kampf.