Wow. I ignore the topic for a couple of days and it all goes to heck.
Where to begin?
1) Japan invaded China, who just happened to be an ally of the U.S.. I find it comical that you refer to an invasion, and a decade long occupation as an 'incident.' Japan was tromping around shooting things long before Pearl Harbor. It was very much part of the war in the sense that it was all done for exactly the same reason: to build the Southeast Asian Co-Prosperity Sphere. You're making a very eurocentric argument there: "Because the war was in Asia it wasn't part of the World War."
2)
Generally, they are regarded as the run up to the war, not part of the war itself. The Rhineland was not WW2
Rhineland? How was the Rhineland a preliminary strike? The germans marched on in, gave a couple of high-fives to the local government and never took the safety's off their rifles. This was thanks, in part, to the fact that the Rhineland was disputed territory anyway, and no one wanted to start a war over it. It was also thanks, in part, to Neville "Appeasement" Chamberlain. He was a winner.
Regardless, the point is that Rhineland wasn't a 'preliminary strike' and it can't be compared to a bloody invasion. Perhaps you could compare the Manchurian Invasion to Poland - Oh wait! That
is when the European war started!
3) Germany couldn't have conquered Britain? It wasn't a sure thing, but odds were probably in favor of Germany. I will most certainly concede that the Battle of Britain went poorly for the Reich, but that's not where things would end. The german army was larger, better equipped and better supplied. The germans were getting darn close to owning the Atlantic before the US came wandering over. It wouldn't have been hard to render the UK impotent. Really, all Germany had to do was surround the islands, wiping out any attempt at a navy, to end the war. You could have gone and bombed the crap out of Germany all you wanted, but, without any possibility of invasion, you would have had little logical justification for it. The most likely event was that Germany would control Europe and make temporary peace with Britain.
3) Russia poses a problem. I would venture to guess that if the Germans weren't so worried about invasion on the west, and all the North Africa business, then they would have taken Moscow in 42.
Furthermore, if Germany wasn't being so befuddled in North Africa, then they would have had considerably less reason to throw themselves on Stalingrad's spears. (Incidentally, even as it was, almost every historian believes that Germany could have done substantially better against Russia if they'd just ignored Stalingrad. It wasn't a question of the Russians being better - they weren't - the Germans just made some really really bad operational decisions.) Anyway, if Germany had been able to get the oil they wanted from the Middle East (by controlling the Mediteranean via North Africa) then they would have had much less reason to go invading the Caucuses.