Complex sentence: Those killings started officially in 1939 and grew steadily throughout the war but many warning signs were already present in Germany well before the war started, including persecution of the Jews, the notorious Nuremberg laws and Kristallnacht in 1938.
Split into simpler sentences: Those killings started officially in 1939 and grew steadily throughout the war. But many warning signs were already present in Germany well before the war started, such as persecution of the Jews, the notorious Nuremberg laws and Kristallnacht in 1938.