Which War was more important?

Franco-Prussian war led to the enmity that drove Versailles into being as harsh as it was, which in turn caused WWII

I must say I agree. Lannes, Japan also played a key role in WWII.

Jean-Luc Picard Actually I think those two things would have remained the same: french-german rivalry with or without the Franco-prussian war and Japan's general direction of expansion with or without Hilter.

Things weren't that great even before the Franco-prussian war for those two nations. Even if France didn't lose to Prussia, a slightly smaller Germany would still maintain a bitter grudge against France for its heavy-handed interventions for the last 100 years or so at that time (and of course, in that same context, Germany had plenty of good reasons to be angry with the British meddling too).

Japan... it was well on its course toward a head to head confrontation with Russia over the east Asia coastal theater like Port Arthur, Korea, and various islands etc. Likewise, the aggression against the colonial powers in the Pacific made America uneasy (we were the colonial powers' ally longer than we were Japan's ally). If Hilter hadn't came into position. Theere would have been still a war in the Pacific, regardless. A different one, to be sure.

The same thing could be said for Europe, it was bigger than just one man. Hilter may have been the biggest influencing singular person but there was plenty of issues bubbling up before WW2 broke out. Hilter made things twisted into his personal agenda, but he didn't create something out of thin air.

I am absolutely certain that the terms of Versailles wouldve been as harsh as they were without the Franco-Prussian War because of all the carnage and death and destruction caused by the war. The massive reparations wouldve needed to be paid still, the territorial concessions would probably be more or less the same, and all of Germany's colonies wouldve been divided. 

Meanwhile, the Shogun of Japan bowed down to foreign powers such as America, Britain and Russia. This would have continued if the daimyos of Choshu and Satsuma did not rebel and start the war. Because they won, Japan became incredibly modernized and was the only East Asian country to resist imperialism and even start an empire of their own. This would then result in the Pacific War between America and Japan eventually.

Thailand did not resist imperialism, they just weren't annexed because they were used as almost a buffer state between French Indochina and British Burma. They had to cede parts of Malaysia to Britain and concede all of their power and influence in Cambodia and Laos to France. China was incredibly exploited, they had to give trading power to Europe, had to cede multiple ports to different European powers, got pushed around by Russia multiple different times, with them invading Manchuria multiple different times, as with Mongolia and Xinjiang. 

Japan was at first subjected to this treatment following Commodore Matthew Perry's expedition to Japan, but following the Boshin War, Japan modernized and was able to be on par with the European powers, even defeating one (Russia).

While the Franco-Prussian War did result in a change of military thinking and displaced France as the leading power, the First World War wouldve remained nearly the same. No Maginot Line, but there would still be trench warfare en masse killing thousands upon hundreds of thousands upon millions, and still resulting in a stalemate. Even if Belgium wasnt invaded, Britain would have more than likely joined France anyways because of their fear of a German superpower and that Germany could eventually outmatch them in every aspect, even the navy. 

The Boshin War. It goes wider and longer.

Any influence of the Franco-Prussian War ended at 1945. In 1945, Germany started with a clean slate. Franco-German enmity is far less now.

However, the Boshin War still has influence today, Japan being heavily industrialized. I dare say without the Boshin War things like the USSR and World War II wouldn't have happened, since Tsushima didn't happen (then the Tsarist government wouldn't have tattered military pride and still have some small respect).

Japan beating Russia was also a boost to many anti-colonialist movements, especially in Asia. Without the Boshin War, the history of Asia and Africa would have been very different today. Europe too.

But if the Franco-German War didn't happen or Prussia lost both the World Wars would have been very different if it happened at all because Germany wouldn't have been such a major power. I dare say the European theatre of WW2 was more impactful (not tryin to downplay what happened in the Pacific but I feel Europe influenced today more than the Pacific) and it wouldn't have been like that if the Franco-Prussian War didn't happen or worse Prussia lost.