Last year I read and watched a bunch of history and military tactics material, mostly focused on World War II. I am definitely not an expert, and I dont suppose my thoughts are 100% correct, but I do have a new and improved understanding of WWII and maybe I can summarize it below.
There are two sections below: turning points, and broad strokes. Turning points are single key events that seem to have mattered a lot, and broad strokes are the big qualitative differences between the two sides that seemed to matter.
- After the official declaration of war in Europe, there was no combat at all on the western front for roughly 6 months. There was a long and unexpected silence in the initial months of WWII. Military officers on both sides noted that their own side was not prepared to defend itself from attack, and how strange it was for there to be no combat given how vulnerable they were. Had the French forces rushed an attack after the declaration of war it is plausible they could have held the Germans back.
- The French and Germans had the previous 2 decades prior to WWII to prepare for armed conflict between the two nations. The French famously built huge defensive chain of fortresses along their south eastern border with German called the "Maginot line". The Maginot line never saw any combat, but this is not because it wasnt effective. The Maginot line was a strong deterrent and it ensured that the Germans would have to attack somewhere else. The Germans had no other practical option for invading France except to through Belgium in the north of France. The French and Germans both had a mutual awareness of this and both of them anticipated the war to start with a German attack through Belgium. That is exactly what would have happened, except for one surprise event leading up to the planned German attack: by dumb luck the French captured a pair of German officers who had in their posession documents detailing the German invasion plans. The German army learned of this, and therefore knew their exact plan had been discovered by the French. To regain surprise, the Germans radically changed their strategy at the last moment. Instead of advancing through Belgium in the north, they would instead advance through the wooded Ardenne mountains south east of Belgium. The Ardenne mountains had been neglected as a possible invasion route by the French, since it was their belief that the terrain was too rough to be traversable. When the Germans executed their new plan they actually travelled through the Ardennes quite easily. Once the French knew the Germans were on their way, the French mistakenly rushed their forces into Belgium to meet the Germans. By time the French and other allied forces realized the Germans were not in Belgium, the Germans had already made it through the Ardennes and into France and were now attacking them from behind. Had the French simply not obtained the German attack plans, or had the Germans not changed plans at the last moment, the French would have likely been better prepared in defending themselves.
- When the Germans snuck around the allied forces during the invasion of France, they pinned the allied forces against the coast line in Belgium. This set the stage for the famous evacuation of Dunkirk. Allied forces were pressed up against the beach, desperately trying to find any ship transport capable of taking them out of Dunkirk, across the English channel and into the allied UK. At that moment of the war, a massive amount of allied forces were totally vulnerable, and the Germans, for whatever reason, did not exploit that vulnerability and instead let quite a lot of allied soldiers escape across the English channel. Had the Germans not let the allied forces slip away, perhaps the strength of the allied army would have been taken from them.
- During the early stages of the battle of Britain, in which the Germans continuously sent their air forces to attack and bomb the UK, they initially targeted British air fields. They wanted to crush the British air force first, and then own the skys over England, whereupon they could have air superiority during a subsequent land invasion. Attacking British air fields proved to be very effective. For a long time, the Germans were winning, and eventually had the royal airforce on the ropes- about to break. There was a turning point in this dynamic however, and it all stems from a misunderstanding. Bombing in this time period was very inaccurate. One German bombing raid accidentally hit a small town instead of the military target they intended. The British didnt recognize this as a mistake, and instead perceived the Germans as cruelly attacking civilians on purpose. So, in revenge, the British decided to bomb the city of Berlin directly; also targeting civilians. The Germans didnt register that bombing Berlin was a revenge strike, and thought they were the first victims of civilian bombing from the British. The German response was to take the gloves off, take revenge, and start deliberately bombing British cities and industry instead of the royal air force. But, it turns out that bombing cities isnt actually that effective in terms of achieving military success. It turns out that bombing civilians just pisses them off a lot, instead of crushing their morale; and bombing houses, unlike bombing airfields, doesnt stop the British from deploying their armed forces. By taking aim at British society itself, instead of the royal airforce, the Germans actually just gave the royal airforce the breathing room they needed to recover, and the Germans therefore switched to a losing strategy. The royal airforce was able to fight back, and push the German airforce back.
- When the Germans invaded the Soviet Union, the Soviet Union was initially losing very hard. The quantity of tanks they lost, for example, was enormous. At the time, Stalin was insisting a kind of no-retreat strategy, which was not working out at all. In practice "no retreat" meant huge quantities of Soviet forces marched directly into German possession. The Germans advanced all the way up to Moscow, to the point where they could see the buildings of Moscow itself. This is around when the tide turned against the Germans. Stalin, after a lot of consideration, decided he would personally remain in Moscow despite the risk that he himself would be captured with the city. This move was likely to inspire Soviet forces: if Stalin retreats, then everyone knows he expects Moscow to be lost, which is both a bummer in itself but also a bummer to see your leadership have such a grim outlook. Anyway, back to Germany. It seems that if the Germans really wanted to, they could have attacked and captured Moscow. The reason they didnt seems to be that they didnt believe it had strategic value. They believed that it was more important to crush the Russian army and to crush the Russian supply chain that supported that army. In the North, the Russians had ports through which American ships could deliver supplies. In the South, the Russians had oil. The Germans figured that those were more important targets, and chose to divert forces from Moscow. But they could have been wrong. Capturing Moscow could have meant capturing Stalin and disrupting the entire chain of command and it could have been spiritually crippling for the Soviet forces.
- The Lend-Lease Act was an American bill permitting the United States to sell weapons to allied forces like the UK, Russia, and China. Its a common area of debate how important Lend-Lease was to the time line of the war, but I think it is fair to say that it is at least plausible that the Soviet Union would have lost very early on in the German invasion had they not been supported by American supplies. But, for this to truly be a turning point in the war, it has to be possible that the Lend-Lease act was not enacted. How plausible was it for Lend-Lease to not get enacted? Well, it made it through the US congress with about 60% of the vote, and according to wikipedia it was favored by 54% of Americans. So, a small majority pulled off the Lend-Lease act. Maybe if the political currents in the US had been different, then it would not have come to be, and the Soviet Union wouldnt have had those critical supplies.
- When the Germans invaded the USSR, they didnt tell their ally Japan about it in advance. Japan therefore, got the opportunity to sit back and think about whether they wanted to participate. And of course, they decided not to, and instead they focused on securing the Pacific ocean. They could have chosen differently, and had they, its almost certain the Soviet Union would have fallen.
- The Roosevelt administration really wanted to go to war with Germany. They couldnt do it, because invading Europe just wasnt popular enough politically; but they still wanted to, so they did what they could to undermine Germany. When Pearl Harbor was attacked, there was no question that the US was at war with Japan. During the scramble after Pearl Harbor, the Roosevelt administration was worried that Japan had basically stolen the political spotlight, and that Americans would no longer have patience or attention for the idea of going to war with Germany when the US itself was under attack by Japan. That all changed entirely a few days later, when Germany declared war on the US. Hitler did Roosevelt's work for him and provided the perfect political context for the US to go to war in Europe. At least some of the high ranking German military officials recognized that decision as the beginning of the end for Germany.
These are in order of most significant to least significant.
- The allied forces were truly unified, but the axis wasnt unified at all. The US, the UK, and the USSR collaborated with each other quite closely during the war. They supported each other and planned together. The axis powers, in complete contrast, did not collaborate or share intelligence. Italy, without any consultation from Germany, declared war on Greece and dragged a reluctant Germany into their mess. Germany didnt tell Italy or Japan they were invading Russia, and Japan didnt participate. Japan didnt tell Germany about Pearl Harbor. The axis powers were generally a victim of their own surprise, as much as their enemies were.
- The allied forces had extremely good intelligence. Allied forces broke the German enigma code. Allied forces were able to effectively listen to quite a lot of German and Japanese communications. The US had detailed and advanced notice about at least the first three important Pacific battles: Pearl Harbor, Midway, and Coral Sea. Generally speaking, the allied forces had a good understanding of what the axis forces were trying to do before they did it, and the axis powers had no reciprocal insight into what allied forces were doing.
- If you just look at the economic numbers, Germany and Japan were quite outmatched. The quantity of resources in the US dwarfed those in the axis powers.
- Germans werent actually all that advanced, strangely enough. This is usually a surprising fact for people, but, a majority of German troops and supplies travelled on horse back. Russia was invaded by German troops who either walked or rode in on horse back and dismounted before attacking. Only a minority (~17%?) of the German army was "motorized", meaning traveling into combat in trucks and tanks. The treaty of versailles limited how strong the German tank forces could be, and the treaty seemed have been effective. The Germans didnt actually have a lot of tanks, and the tanks they did have were kind of dinky for their era.
- Germans and Japanese made a lot of decisions about military tech that seem pretty questionable in hindsight. The Germans and Japanese had the largest battleships in the world, the Bismark, the Yamato and the Musashi. The Bismark sank one British battlecruiser and then was subsequently destroyed by 16 old fashioned biplanes. The Yamato and the Musashi basically spent the entire war running from American aircraft and didnt actually do much damage during their lifetime. I think big battleships were outdated in WWII and the axis didnt realize how vulnerable they were to aircraft. Both the Germans and Japanese made super huge investments into enormous ships that did not pay off at all. The US and the UK invented large long-range bomber planes that did a ton of damage and the Germans and the Japanese never invented an equivalent bomber. In fact, instead of building bombers, the Germans invented the V2 rocket to fly bombs from Germany to England. The V2 rocket worked, but it made no sense from a cost / benefit perspective: they would build an entire rocket to deliver one bomb payload. Consider a bomber, that is simpler technology and can drop payloads repeatedly assuming it is not shot down.
- German and Japanese logistics dont seem to have been all that optimal. For example, every German tank was basically a work of art. Every German tank was perfectly manufactured. Every German tank model was completely original and had every component developed from scratch. This kind of attention to detail is just not a productive way to fight a war. Every new part requires new production methods and fresh research and development. Whenever you introduce a new tank into your army, you need to make sure engineers on the front lines will have a supply of parts to fix their tanks with and its just harder to do that when there are more kind of parts for more kinds of tanks. Americans had fewer tank models, and the different models shared a lot of components, so American tanks got better maintainence. There was more collective wisdom about how American tanks worked, because their use was more widespread. Russian tank logistics operated in the same way as the American tank logistics I think. Furthermore, Russian tanks were basically hastily slapped together and then driven out the door of the factory into the fight. They correctly didnt have patience for perfection. It seems like where German planners were thinking "What makes for a good tank?" Soviet planners were thinking "How do I turn steel into defeating the Nazis?" whereafter they put together any kind of vehicle that got the job done. Changing focus to the pacific, US submarines were large and powerful and very effective at disrupting Japanese logistics. The Japanese could have protected them more, but they didnt. The Japanese didnt reciprocate with their submarines either; in fact they used submarines for a different purpose entirely: to try and sneak supplies around the pacific. The Japanese went through dire efforts to resupply troops on various pacific islands, like Gaudalcanal, and they lost tremendously in doing so. The interesting part isnt that they lost so much, but more that they lost so much for dubious gain. It is unclear that owning islands in the ocean provides strategic value. Owning an island isnt necessarily like owning a fortress. The ocean is big and empty, and if you own a little pacific island you arent positioned to block the travel of your enemy around your island. It seems like they had their priorities in the wrong places.