Warmatrix

The Fall of France of 1940 CE, part of World War II, elevated nazi Germany to the status of superpower. In sharp contrast to the mirroring German-French battles in northern France in World War I, it was over in less than six weeks.
After Germany invaded Poland in September 1939 CE, both France and Britain declared war. After success in Poland Adolf Hitler wanted to turn west right away, but was warned by his generals that the army was in no state to mount another major offensive so soon. Neither were the western armies. During the winter nothing much happened, hence that period was called the 'Phoney War'. That changed in April of the next year, when Germany quickly overran Denmark and Norway. With the north secured, the attention turned to the main target: France.
In World War I the Germans had also launched an offensive to the west. That time their strategy was the 'Schlieffen plan', a sickle-maneuver through Belgium into northern France, which came close to success but failed to make a decisive breakthrough. Between the two wars France, with lower manpower reserves than Germany and determined not to be forced to fight on its own soil again, had invested massive sums in the Maginot Line, which ran along the French-German border. The German high command realized they stood little chance of overcoming this defense. The first version of its plan, Case Yellow, envisioned another attack through Belgium, advancing up to the river Somme and pushing further on two years later, when the strength of the German army would be greater.
Hitler did not agree and wanted a faster, more aggressive approach. General Erich von Manstein, Heinz Guderian and others revised Case Yellow. In what is often called the Manstein plan, half the army would attack the Netherlands, occupying it as a base for later attacks against Britain and simultaneously advance into northern Belgium. A second branch would move through the difficult terrain of the Ardennes and break into France at Sedan, race towards the sea and cut the allied armies in two. It was a risky strategy and the German generals were heavily divided, but Hitler approved it. Most of the forces available to the Germans were assigned to the task: 135 divisions, 2,400 tanks and 7,400 artillery guns, while the Luftwaffe provided 5,600 aircraft. The army was still in the process of being built up. Only 10% of the forces were motorized; at least half of the tanks were feeble Panzer I's and Panzer II's. But the Germans made good use of radio to communicate on all levels: among vehicles within units, among units themselves and throughout the entire army. This gave them good tactical flexibility.
The allies, expecting another years-long war like World War I, were still playing for time and building up their strength. They also prepared for the German offensive, expecting another Schlieffen-like attack. The French aimed, at the first sign of trouble, to advance into Belgium with their best units and hold the Germans there, at the Dyle line. The combined armies of France, Britain, Belgium and the Netherlands numbered 141 divisions, 3,300 tanks, 14,000 guns and 2,900 aircraft in the northern France and the Low Countries. Most of the strength and almost all tanks came from the French. However the tank battalions were not trained to work together with the infantry, greatly reducing their effectiveness. Communication inside and among the armies, burdened by cumbersome hierarchical structures and relying on vulnerable telephone lines instead of radio, was poor.
The German attack was launched in May. Army Group A overran Luxembourg almost unopposed. Army Group B tried to to bypass Holland's traditional water defenses by landing paratroops in the west, while the main force invaded from the east. This was only partially successful and the Germans tried to break the resistance by bombing Rotterdam. The Dutch surrendered, but the bombardment went ahead anyway, under vague circumstances. Meanwhile other paratroopers captured the Belgian fortress of Eben-Emael, paving the way for the ground troops. The Germans advanced much faster than the allies had anticipated, though received a brief check at the tank Battle of Hannut.
Meanwhile the German Army Group A struggled to drive through the Ardennes, leading to long traffic jams. The vehicles were sitting ducks for air attacks, but the French had removed most of their air force to airfields far behind the frontlines. They had more or less anticipated an attack through the Ardennes, yet severely underestimated the speed of the German advance. A combination of close air support by the Luftwaffe and weak French resistance allowed the latter to break through at Sedan. Soon after their commanders, Heinz Guderian and Erwin Rommel, were ordered to stop and reorganize, but they ignored the command and in true 'Blitzkrieg' style pushed on. The allies mounted a few counterattacks, however did not concentrate their forces properly like the Germans did and failed to dislodge them. The superiority of the allied tanks was offset by poor communication and German 88mm guns.
Now surrounded on two sides, the position of the British Expeditionary Force was precarious. It retreated towards Dunkirk, while Belgian and French forces fought delaying actions, and then was evacuated back to Britain. By the end of May, Case Yellow complete, the allies had lost 61 divisions and most of their armor, guns and aircraft. France had to cope with millions of civilian refugees streaming south. Italy declared war on France too, but was effectively blocked by French troops in the Alps.
In early June the Germans renewed the attack, launching Case Red against the center and south of France. This time the French resistance was much better organized and at first they resisted fiercely. However they had already lost too many men and too much equipment. After a few days, they were forced to retreat and after two weeks the defense collapsed. Paris was declared an open city, to spare it the ruin of a siege; the rest of the country soon followed. The French were forced to sign an armistice and their country was reduced to a rump state in the southeast: Vichy France.
German army losses are estimated at 27,000 killed, 111,000 wounded and 18,000 missing. The Luftwaffe lost about 1/3 of its strength in combat and accidents. French losses were much higher, around 85,000 killed, 12,000 missing, 120,000 wounded and 1,540,000 taken prisoner. Britain had 68,000 casualties and lost most of its equipment; almost 1,000 aircraft and 1,500 pilots; 240 ships. Belgium lost 6,000 killed, 16,000 wounded and 200,000 taken prisoner; the Netherlands 2,300 killed, 7,000 wounded and 270,000 prisoners. There were even losses on the Polish side, as Poles fought side by side with the western countries: 5,500 killed and 29,000 taken prisoner. Case Yellow proved as risky as some generals feared it to be; if the allies had coordinated their counterattacks well, they could have crushed the relatively weak German panzer forces. But they did not. Superior communication, combined arms tactics, air power and relentless momentum made sure that the German victory was never in real danger. The world realized that the trench warfare of World War I had been replaced by something new.