Short answers, pulled from the story.
The Reichswehr was the official name for Germany's armed forces during the Weimar Republic and the first two years of Nazi Germany. It was officially formed on the 1st of January 1921, after the terms of the Treaty of Versailles had been met, with the Defence Law of the 23rd of March 1921 regulating its structure.
Under Part V of the Treaty of Versailles, the Reichswehr was limited to a professional army of 100,000 men and a navy of 15,000. The treaty also prohibited the establishment of a general staff, heavy weapons above defined calibres, armoured vehicles, submarines, large warships, and any type of air force.
The Black Reichswehr was the informal name for illegal paramilitary groups, known officially as Arbeits-Kommandos, organised by General Hans von Seeckt in 1923 and attached to Reichswehr units. Drawn largely from former Freikorps members, the Black Reichswehr reached a peak strength of about 20,000 men, allowing the Reichswehr to secretly exceed the Versailles Treaty's 100,000-man limit.
Following secret negotiations in Moscow in February 1923, the Reichswehr established training facilities on Soviet soil. A secret aviation school at Lipetsk trained approximately 120 military pilots and 100 aerial observers. Tank specialists were trained at Kazan starting in 1930, and chemical warfare agents were tested at the Tomka site near Saratov.
When the Kapp Putsch threatened the government in March 1920, almost all Reichswehr generals, led by Hans von Seeckt, advised against deploying troops to defend the republic. Seeckt was reported to have said, 'Reichswehr will not fire on Reichswehr'. Only General Walther Reinhardt recommended using army troops in the government's defence.
The Reichswehr was renamed the Wehrmacht on the 16th of March 1935, the same day Adolf Hitler reintroduced universal conscription in violation of the Treaty of Versailles. On the 1st of June 1935, its army branch, the Reichsheer, was renamed the Heer, and the Reichsmarine became the Kriegsmarine.