One German word... Lebensraum. The idea that Germany needed to expand and displace "inferior" races to make room for "superior" ones. Make no mistake, the British/French/etc were considered part of the "superior" races, that does not mean Hitler didn't want to just leave France and Britain alone. True, early war he did try forcing peace with Britain, but that was only a stalling move so that he could deal with his ideological enemies in the east. Like his first steps - Austria, Sudetenland Czechoslovakia, the rest of the Czechs, etc, Hitler would have kept making demands. Assuming a policy of appeasement continued and never ended, and assuming Hitler beat the Soviet Union, Britain would have eventually be isolated and it would have been, "Surrender peacefully to the Third Reich or prepare for war."
Now how long his ideology would have carried on with successors to his empire is another debate.