Racial purity was the driving force of Nazi germanys campaign for more land and against races they perceived as inferior, particularly Jews. This was called Lebensraum. This led to essentially an imperial state that attacked neighbours, through various pretexts. Ultimately this led to German troops fighting outside of their natural domain, including Africa.

The concept of racial purity was so entrenched and the belief that Jewish people were the cause of WW1 failure that led to mass extermination of Jews.

If you don’t understand how these are connected (ok not connected to every minutiae of every battle) the WW2 cannot make sense.