No major war in Europe in the next ten years (?)

Military history is just like general history an excellent tool for learning. You cannot make enough personal experiences to match what history offers you.

History offers valuable lessons for our strategic situation today. We feel extremely safe from threats of conventional war in Europe, and see no conflicts that could lead to such a conflict any time soon. Finally, we don't believe that any other power could challenge us in Europe - after all, we would have nukes for the worst case that our conventional forces fail.

There are two very disturbing lessons in military history that offer parallels to this situation.
I scratched on the surface of these lessons before, but they deserve a more thorough presentation.

I never truly believed the "nobody attacks us because of our nuclear weapons" ideology.
Air war theorists expected massive genocide from the air with gas bombs for the next war in the inter-war years (1919-1939) - but there was next to no poison gas usage in World War II. Hitler had the very first nerve gasses under his control and thereby a considerable advantage. But he never used any gas. Even not when the conventional attacks on England in 1940 failed or in more dire situations afterwards. No other power used gas in quantity on the battlefields or for bombing cities.
This means that there's an historical example that matches our expectations of 'WMD' dominance in the next European major war - and this example tells us that such expectations don't need to become reality.
We should (stay) prepare(d) for the case that some nation calls our nuclear deterrence bluff and not rely much on the nuclear deterrence.

The other remarkable and very irritating lesson of 20th century history is that you cannot plan your forces as much as five years in advance. To attempt it and stick to the plan leads to failure in case of real need for forces.
Germany had a 100,000 men military army in January, 1933. There was no military aviation allowed. And these troops were all volunteers, conscription was forbidden. There had been no training of reserve troops for many years by 1933 and the World War veterans weren't fit for combat service anymore.
Less than seven years later Germany had the most powerful army, a small but dangerous navy and an air force that was better prepared to support army operations than any other air force in the world. This rise of a phoenix shows how quickly a strategic situation can change.
Our policy would have a serious lag before it recognizes and reacts to such a challenge as did the policies of the European nations in the 1930's. The power which prepares for war in a specified time frame can more easily build up a modern and ready force than such a force can be maintained for decades.
The similarities between 1933 Germany and today's Russia are striking.
Mortified, defeated, survived economic crisis, shrunk military, authoritarian government, desire for national greatness, territories to reclaim, history of military strength even without major allies, arms limitations treaties in force...let them ally with PR China and they could grab Eastern European territories just like Germany was able to grab Saarland, Austria, Czechoslovakia and Memel before appeasement was given up. Imagine a reunification of Russia, Belarus and Ukraine. We'd quickly face a nation much stronger in population, geo-strategic means, economy, arms industry and military - and probably backed up by an allied China.

The feeling of complete security in Europe and the assumption that it would require decades to threaten us with conventional war is completely wrong. History's lesson is clear-cut: Such safety cannot exist, there are historical precedences for what it would take to create a conventional total war in as few as a couple years.

S O

edit: Corrections about Reichswehr size were made.