In early November 1939 the world watched as a false-flag event in Silesia prompted Germany to demand from the Poles that Danzig be returned to Germany or face war. Poland, having recieved guarentees from the Allies, quickly rejected and mobilized for a conflict - yet would soon realise they were hopelessly outmatched. Striking in a spearhead south from Slovakia towards Krakow and north from lower Silesia towards East Prussia, Polish forces were quickly dismantled by the German army that defeated the country in 9 days and 22 hours, capturing Warsaw and Krakow before even the fall of Danzig at a loss of only around 12,000 men. Sensing French weakness, German planning quickly turned to the invasion of France, executing a plan to seize the low countries in a rapid armoured strike through Limburg and into the unprotected Belgian rear, and with a seperate strike through Luxembourg and the Ardennes.
The plan initially went off without a hitch, paratrooper forces landed in Antwerp, seizing the city in a surprisingly bloody but worthwhile battle that distracted Belgian forces while the Armoured spearhead seized Maastricht and crossed into North Belgium. Belgian forces, primarily dig in around the German border, quickly were surrounded as light armour, complimented by medium armour divisions to break up enemy lines, punched through and seized Brussels. In the south, German armour easily overwhelmed Luxembourgian forces and pressed on into the ardennes where they met little resistence on account of German paratrooper landings in Glider planes in the region, preventing French delaying advances. German Paratroopers additionally would land south and west of Sedan, yet would meet brutal resistence by French soldiers on the extended Maginot line who fought tooth and nail to prevent the Paratroopers organizing as it would allow attacks on Sedan from both the north, east, and south. German armour did eventually arrive at Sedan, but met constant delays resulting in a drawn out battle that initially looked as though it may stall the German advance completely. Thankfully the presence of a single German Grosstraktor Heavy Tank division allowed the breaking of the French line and a rapid advance to cut forces at the Maginot off from the French forces in the north that had dug in on the Belgian border. British forces, fighting a losing battle in Malaya and Burma, were not deployed to France bar one division with limited air coverage being provided - essentially dooming the French defence by conceding the Germans full air supremacy.
The Netherlands quickly would be whittled away by the German 6th Army that seized Amsterdam in early February 1940 prompting the Dutch surrender in Europe, though they would go on to play a major role in the far eastern theatre. German forces advancing from Maastricht and Brussels meanwhile soon reached their strategyc target of Roubaix, northern France. Here, the flat land, combined with the relative salient of the province in the French line allowed German forces to relentlessly press on the French line in a bloody battle that saw French forces desperately hold off German forces despite the collapse of their line at Sedan. Attacked by air and by paratrooper forces in their rear, the line eventually buckled resulting in the total collapse of the extended maginot line and the disintegration of the French army that quickly became overwhelmed as French forces attempted to flee the country, hotly pursued by German armour that sought to seize the channel ports before they could get to sea. While a secondary line was attempted on the Loire river, crossings at repeated points soon compromised the defence and the battle for france was essentially lost... except for in Paris. Despite the flight of the French Government, six Motorized divisions of the French army refuted the order to leave Paris an open city and fought tooth and nail to protect it, resulting in over a month of brutal fighting as ten German infantry divisions and two armoured divisions tried repeatedly and failed repeatedly to break the city, only doing so after having captured almost all of France anyway and once Paris had been turned into a mess of rubble. This did however allow some French divisions to escape, notably including several cavalry divisions which would play a vital role in the Libyan campaign of 1940 against Italy.
Italy meanwhile had been fighting their own war against the French with significant early success. Despite the best French efforts and some Italian defeats, Italian forces soon proved capable enough to drive the French back as far as the Rhone River, securing a significant chunk of France for their own occupation while also claiming Corsica. In North Africa however the situation was somewhat more dire, with the strategic decision having been made to abandon Ethiopia pre-conflict, the battle over Tobruk proved a challenge to the ultimately outnumbered Italians who faced armies from across the British Empire. Despite having medium tanks and having made headway in Tunisia, Italian forces proved incapable of being able to break the British frontline into Egypt, instead facing a counter attack that began with the landing of four French cavalry divisions on the Libyan coast, capturing key Italian ports early in the conflict and before the fall of France. This led to the strategic decision to flee Libya entirely, with Italian tanks leaving Tobruk only days before British forces surrounded six Italian infantry divisions in the town, ultimately destroying them a few weeks later. Italian forces in Tunisia would manage to escape, allowing Italy to save face in what was a costly and failed campaign.
Axis attention now turned to two new theatres; Yugoslavia and the nordic countries. Germany began early by invading Denmark and Norway in a daring and risky Operation Weserubung that involved landing infantry in Copenhagen and invading the small country from the south, while simultaneously landing seven Fallschirmjager divisions in and around Oslo to capture the port there using gliders. This, thankfully for the German high command, went off without a hitch, immediately leaving the British with the decision not to try and help the Norwegiens and beginning a three month infantry campaign by in the mountainous country to secure it, culminating with the surrounding of over 90% of the Norwegien army at Trondheim in May 1940. Yugoslavia too would soon feel German aggression as the Government of Prince Paul opted not to join the Axis, resulting in the quick invasion of the country in the same month. Britain too would begin to feel the heat hit home as German forces began bombing Britihs factories across the south of the country; aided by both light and heavy fighters, Germany would retain air superiority over Britain for years but would never attempt an invasion due to the entry of the United States in the war in January 1940.
In Asia, meanwhile a decisive battle for the survival of the British Empire in the east was ongoing. British Imperial forces had managed to stall Japanese advances into the Malayan penninsula earlier in the year, with the Japanese trying but ultimately failing to land several marine divisions in Singapore harbour to break the deadlock. American forces would enter the fray in January 1940, with divisions being deployed to both Britain and India when President Roosevelt finally managed to convince Congress of the importance of American support for Britain due to the sheer intensity of German and Japanese aggression, an act that probably only occurred due to the high level of cooperation between Britain and the United States after Prime Minister Winston Churchill came to power in the aftermath of the annexation of Czechoslovakia and failure of the Munich agreement. Meanwhile Japanese forces continued to drive into Burma, though this would not prove the decisive battle of the campaign. That would instead come when Japanese forces landed successfully in south India at Chennai, deploying around 24 divisions to the region and quickly sweeping up much of the south in a surprise offensive that the British struggled to face. This would change quickly though when a Dutch marine division based in India successfully landed in a counter-naval landing at Chennai, taking the port from the now overextended Japanese forces and in doing so cutting their near enough sole source of supply. While Japanese forces would immediately begin work on a new port further south, this proved fatal for the Japanese units in the region which could not be supplied by land, sea or air. This ultimately resulted in the destruction of a vast swathe of Japanese divisions, a massive loss for the Japanese who immediately pivoted to a defensive doctrine, especially following the loss of north Borneo by the Japanese to dutch units.
the only other final development in Asia would be a minor Soviet conflict in north west China, with the Soviets invading the region only to return it to the control of the now strengthened Chinese communists who had made territorial gains from the Sino-Japanese war.