After completing the wonderful "The Rise & Fall of the Third Reich", it dumbfounds me how the world stood by and let Nazi Germany rise in strength and rampage central Europe. Agression dealt with in its early stages could have prevented millions of deaths and the later suffering of millions behind the Iron Curtain. Europe was dealing with the monstrous hangover from World War 1, and many world leaders made moves that they thought would prevent war. They would avoid small skirmishes that could have prevented the big one just to give themselves time. Part of it comes down to Hitler's nature. He was crazy and driven to conquest. This should not have been a surprise to anyone after his 600+ page book on his goals for conquest. No one took him at his written word, and constantly deluded themselves with his broken promises, which racked up over the years.
There were 4 major points where Nazi Germany could have been stopped in its tracks sparing millions killed by warfare and genocide. In chronological order....
1. When Hitler ordered the Rhineland occupied, the 300,000 troops of the French army could have overrun the small contingent of German Troops used for the occupation. Hundreds of thousands of troops at their disposal, but the French did nothing. After countless History Channel specials, books and stories from my grandfathers, the behavior of the French leadership prior to and during WW2 was despicable. This simple chase of the Germans was easy to accomplish and was a strict enforcement of the Versailles treaty. Hitler would have lost face and his support would have been weakened, possibly leading to overthrow.
2. When Hitler gave Austria's chancellor Schuschnigg a week to answer on the Anschluss, Schuschnigg could have coordinated a resistance in Austria with the support of the Czechs and French. If the Austrians had arranged for the French and Czechs to attack Germany if the Austrians were invaded, Hitler would not have invaded Austria, and had he invaded Austria, the combined resistance within Austria and attacks on the west and east from France and Czechoslovakia would have destroyed the Wehrmacht. This might have been tougher to accomplish as it would rely on the Austrians coordinating with the Czechs and the Czechs to get the French to honor their treaties. A loss for Germany would have collapsed Hitler's regime. Game over.
3. Rather than the appeasement of Nazi Germany at Munich, a coalition of resistance could have offered Germany an ultimatum that any attack on the Czechs would be met with attack by multiple countries on the oceans, in the airs and on the ground. The Czechs had fortifications so strong the German generals later said they could not have penetrated them at the time, and the Czechs had a huge army called up for the fight. This was on Germany's east wing. To their west was France and hundreds of thousands of troops. On top of this, The British could provide a Naval blockade and bombers, and the Russians, who were not needed, could have provided help in the air if needed. Faced with an ultimatum from so many countries, the German generals would have overthrown Hitler.
4. A last moment for peace was out there. Had the British and French teamed up with the Russians in the summer of 1939 to guarantee Poland and come to one another's aid in conflict with Germany, there is no way Germany would have attacked Poland. The key here was getting over the fear of the Russian Bolsheviks that the British had, and to convinve the Polish to accept Russian help. I think a simple "you accept their help or no one helps you" would have worked. This would have kept Hitler boxed in, and encouraged other small countries to trust in the Anglo-Franco-Russo alliance.
Alas, it is the past and cannot be changed. We can only wonder what if........