A few points:

1) The whole notion that Nazi buildup and W W II have anything at all relevant to North Korea today, is a total non-sequitor.

2) I actually agree with some of what Juche has to say about there being huge misconceptions about Hitler's motives and actions leading up to World War II.
Many of those misconceptions about Nazi objectives, and errors by the allies that led to the most devastating war in history in 1939, are explored in Pat Buchanan's new and heavily sourced and documented work, Churchill, Hitler and the Unnecessary War, released just a few months ago.
Mussolini despised Hitler, but was forced into an alliance with Hitler, when he was isolated (primarily by the British) and had no other allies, and thus reluctantly signed a pact with Hitler.
Hitler was largely simply reversing the unjust terms of Versailles Treaty, in the 1933-1939 period, until the door to further negotiation was closed to him by the British.
While Poland was ruled by a dictatorship, and seized the richest mining area of Czechoslavakia in March 1939, Britain vowed to defend Poland, while Poland was arguably as Guilty as Germany in carving up Czechoslavokia.
Hitler negotiated with Poland and saw them as a potential ally against Stalinist Russia. From March to August 1939, Hitler offered again and again to resolve the Polish Corridor issue with Poland, wanting only the port city of Danzig (400,000 people, 95% German) and was willing to let Poland KEEP the Polish Corridor and the 1.2 million Germans there, in exchange for Poland allowing Germany to build railroad and highways over the Corridor to connect Germany with East Prussia peacefully.
Which was a very reasonable offer.
But the British signed a war guarantee with Poland, guaranteeing Britain would send troops to defend Poland if invaded by Germany, despite that it was a completely hollow guarantee and a bluff, with no ability by the British to back Poland with military action. And with a war guarantee, Poland refused any further attemps to peacefully negotiate even the most reasonable terms to resolve the Danzig and Corrisor issues.
Even after Nazi/Soviet invasion of Poland, Britain could have sued for peace after Dunkirk, and Hitler would have gladly accepted. Because war in the West was just a distraction from invading Russia, his true and clearly stated objective.

Britain and France went to war to save 6.5 million poles from German occupation, but then ultimately, Churchill in 1945 (Potsdam and Yalta agreements) signed away 100 million East Europeans to enslavement by the Soviets. And Britain and France lost their wealth and global empires in the process. Which hardly seems worth it.

The right action would have been to let Germany invade Russia (as clearly envisioned in Mein Kampf, Hitler's goal of lebensraum, "living space", expansion east into Russia, and Hitler considered Communism the greatest threat to Germany, that had to be eliminated). As was inevitable, let the two brutal dictatorships clash as Stalin and Hitler both planned, let the two exhaust each other. The British and French democracies would have survived the war in the sidelines unscathed, and reaped the benefits of their enemies ceasing to be global players, or any further threat to them.

Similarly, invading North Korea now would be a waste of men and resources and inefficient, while other methods exist to neutralize North Korea and its nuclear ambitions.
Japan and South Korea are the ones threatened by North Korea's nukes and million-man army, let them invade, if someone has to. They have huge economies, both, and can easily afford their own defense. Each has at least 40 times North Korea's economy and resources, more than enough to defend themselves.
If China thought we would allow Japan to get nuclear weapons capability, they would react to that threat by immediately clamping down on North Korea. And since North Korea is completely dependent on China for energy, food, and its economy, it would be like shutting off a switch in China, to bring N. Korea to its knees within days.
Alternately, If the status quo were simply maintained against North Korea, maintaining their military consumes a huge percentage of North Korea's economy, and is unsustainable. Force them to sustain it indefinitely, and their state will collapse under its own weight, as the Soviet Union did in 1989-1991.

But either way, there are many ways to cripple as fragile a state as North Korea, short of an all-out frontal American assault.

At most, we need only bomb (conventionally) North Korea's nuclear facilities, eliminating their ability to create or proliferate nuclear technology to other countries. It is only North Korea's proliferation potential that would warrant any military action.