I don't think you can really compare the British Empire to Germany in the long run. While the world wars accelerated the breakup, it seems to me that it was bound to happen. So it's a question of comparing the long term performance of the UK to Germany. And Germany wins here. Colonialism generally wasn't going to last for anybody.
The German General staff had convinced themselves that preclusive war against Russia was necessary, true, and it is also true that Russia was growing very fast and that its military potential would grow with it. But given their two front situation, Germany would have been better off seeking a defensive solution, and detaching the British from the French and Russians, not invading Belgium, etc. Keeping Italy friendly or at least neutral would also be a good idea. Wilhelmine Germany's diplomacy was amateur hour.
Japan is an interesting case here as well. They actually "won" the peace post WW2. Showing that their previous policy of colonialism and economic autarky was unnecessary and self defeating. Although they now have a terrible deflation problem that should have been addressed long ago. (BOJ finally has decided to get serious about this.)
Not in the long run, perhaps, but Nazi Germany was a product of, and confronted, two old empires that dominated the world and its trade.
Indeed, nothing lasts, colonialism included, but in the ebbs and flows of history, one cannot rule out bouts of neo-colonialism, even. Having different causes from old colonialism and taking place in a very different world, they will not be the same, but in the sense of occupying or controlling territory for the control of various resources and the denial of these to rival powers, history is far from finished with colonialism.
I really don't believe Germany was ever in position to fight defensive wars last century, not in the context of its needs and enemies. Britain has always followed a policy of supporting a weak continental power against the dominant one, for obvious reasons. I am well aware of Britain's dynastic ties with Germany, and after WW I, enthusiasm among much of the aristocracy and middle classes for fascism, not least Lord Halifax's faction, which wanted peace with the Nazis. That said, these sections of society were not formulating policy and they lost out because other, more powerful sections of the establishment were entrenched in a policy tradition that had worked for centuries. Churchill was a great leader of his class and he won that leadership because his policy had deep roots which were not yet ready to shift.
That being so, Germany last century could not have split Britain from France. So long as they remained united, starvation was always going to be the result of a long, defensive war. If the Kaiser didn't, Hitler definitely knew it. In WW II it is true that Nazi racial theory allowed the calorific deprivation on the continent to be concentrated in sections of society deemed 'sub-human' but this was not a long term solution. The basic fact is that Europe could not attain calorific self sufficiency with the prevailing methods of agriculture, if it ever could.
Yes, Japan was also a winner, but that doesn't prove their previous policies were unnecessary. Autarky has long been used as a shield from an intrusive and powerful outside world. The peace imposed on the world by the US, then the world's biggest creditor nation, completely changed the game. Bit by bit it's been unravelling ever since, but it made possible the massive expansion in productivity and wealth that lasted into the 1970s.
Japan's been unable to solve its problems for decades, but not for want of trying. It was the 'carry trade' of low interest money from Japan to the US that helped inflate the speculative bubble that burst in 2008. Trouble is, you need to produce values to sustain a capitalist economy, and sell them at a profit. The powers that came out of WW II on top, today predominantly speculate and borrow. Germany is the exception, but Germany too, must find resources and markets.
“The end of democracy and the defeat of the American Revolution will occur when government falls into the hands of lending institutions and moneyed incorporations.”
¯ Thomas Jefferson