The Kapp Putsch or The Weimar Republic stillborn
After considerable internal debate, the Freikorps fully support the Kapp Putsch, and successfully capture the government of the Weirmar Republic before they can issue the call for a general strike that crippled the Putsch OTL. The Putsch prevents the money fallout, and keeps the middle and upper class in their support. The Allies are too tired and burnt out to make a move against Germany now, Britain is at war in Ireland, and Poland is currently at war with the USSR. The Putsch causes communist agitation and violence to increase dramatically over OTL, but this makes the conflict briefer, with the Kapp government taking total control of Germany by 1925. Rather than disband the Reichstag, the Kapp government manipulates the election process to keep the Reichstag packed with rubberstampers who effectively marginalize the power of the Reichstag.
To placate the Allies, the Freikorps are "disbanded" or become "civilian organizations in private hands" I.e. former Army officers supported by upper class money. Resurrecting a Prussian tactic from the Napoleonic Wars whereupon they, with a limited army, recruit people for a few months, train them, and then let them go, but always on call. This gave them a base of trained people to draw on when needed. Here, the Germans do the same thing, slowly building up whole hidden regiments so a whole army can be assembled quickly.
Nominally, the Kapp government follows the barest of the requirements of the Treaty to keep the Allies complacent; though France still builds the Maginot line, only 10 years earlier, and bankrupts themselves doing it; beginning in 1920, completed in 1926; however this Maginot Line is less advanced and capable than OTLís.
In response to this sudden change in German politics, the Allies start pumping out more WWI tanks, with few improvements throughout the 20's...while preparing some advanced prototypes. When the Crash hits, they abandon the advanced designs, hoping that their overwhelming number of older tanks will end the fight quickly
The Kapp government ends in 1922 with the death of Wolfgang Kapp from cancer. He is succeeded by Alfred Hugenberg as the public head of government; his experience as a media mogul gives him considerable skill as the public mouthpiece and political figurehead of the regime. Luttwitz is the effective head of the government, officially the Minister of Defense, until late 1941 when he retires due to poor health, he is succeeded by Kurt von Schleicher, who is accompanied by Franz von Papen as the Foreign Minister.
1923: The attempted Munich Putsch by members of the infant National Socialist party who believe they have the true vision for the future of Germany, it fails when the government orders the plotters put down by force. The handful of survivors are executed for treason against the state.
1927: The beginning of military cooperation with Nationalist China while selling armored vehicle designs to Japan serves as excellent testing sites of arms, tactics and soldier experience; Germany trains the Nationalist Chinese against the Communists, particularly Paul von Lettow-Vorbeck whose considerable experience as a guerilla commander lends him equally considerable expertise in countering them. Under the German advisors, the Nationalist Chinese become well-trained, disciplined and organized soldiers.
Japan on the other hand receives limited aid in the form of light armored vehicle designs and prototypes which often find themselves serving in Manchuria and Northern China; some German advisors use the Japanese to test some early armored doctrines, which the Japanese put to limited use.
In 1931, when Japan initiates the Mukden incident, and invades Manchuria they are met with organized, effective resistance from the Nationalist Army, prompting the deployment of the German-designed Type 27 (essentially a modern light tank). The Nationalist Army resists considerably, but lacking the weapons to counter the Japanese Type 27ís, the Japanese advance.
Japan is shocked at the level of resistance that the Chinese are able to mount, and are also pleasantly surprised by the battlefield performance of the Type 27; prompting a plan for a stronger push into Manchuria, and increased production of the Type 27.
On the other side of the political battlefield Chiang Kai-Shek is impressed with the performance of his army against the Japanese, and his orders to resist the invaders prompt a considerable rise in his popularity amongst the people. Reports of the presence of the Type 27ís and their effectiveness prompts an offer to purchase from Germany (and the Allies) anti-tank rifles and ammunition.
The only exception to the total destruction of the Beer Hall Putsch plotters is Ernst Rohm, who survives the Beer Hall Putsch by using his contacts during his time in the Freikorps; as a result he is sent into a sort of exile in Bolivia as a military advisor. In 1928 Rohm is recalled to Germany after long correspondence with his superiors, convincing them of his innocence in the events of the Beer Hall Putsch. Over the following years Rohm makes many contacts within the various Freikorps and the tattered Socialist Underground, and attempts his own Putsch in 32í. Composed of sympathetic portions of the Freikorps and the last remaining Socialist and Communists in Germany, the Putsch fails after a month of scattered light fighting when the German people as well as the Reichswehr and Freikorps suppress Rohmís "Stormtroopers". Rohm is captured in the last bit of fighting, a very brief affair, and is taken to a military tribunal for trial. The trial is extremely brief, and ends with Rohm being sentenced to death by hanging the next day. With the news of Rohmís execution comes the announcement by President Hugenberg that Germany will begin open and immediate rearmament of the Reichswehr and the reintegration of the Freikorps into the mainstream Army. The very public rearmament of the Reichswehr is accompanied by the very, very quiet purging of the Freikorps of all possible Rohm supporters.
In the months after the Putsch and the rearmament, the Japanese restart their offensive in Northern China with more Type 27ís and even more soldiers as well as heavy airpower. However, the long break before restarting the offensive has allowed the Nationalist Chinese Army to deploy their handful of anti-tank weapons in concentrated areas...