Why do you think Hitler decided to invade the Soviet Union before defeating the British (or ending the war on the western front)

Why do you think Hitler decided to invade the Soviet Union before defeating the British (or ending the war on the western front), effectively creating a two-front war that Germany had successfully avoided in the first years of the war? Considering the documents you read, was the war between the USSR and Nazi Germany inevitable, or was this a tactical error by Hitler?