In OTL, we know that Hitler was motivated by the "stab-in-the-back" myth: that Germany had not really been defeated by the Allied Powers in World War I, but betrayed by Jews and socialists on the home front. It was for this reason, amongst many others, that the Holocaust happened.
But what if Hitler was instead motivated by a desire to seek revenge against the UK and France for what they did to Germany in World War I?
This Hitler plans to invade and conquer both countries, and then have them thorougly dismantled and absorbed into a Greater German Empire. In TTL, British and French people would be treated like the Jews and Slavs in OTL.