Lots I guess....ranging from the Ebert-Groener Pact, the influence of von Seeckt in the early years, the election of Hindenburg and the growing impact of army advisors in his inner circle, the political role of von Schleicher and if it extends to the Nazi regime, you got the fact that it was the only insitution that would (initially i.e) have had the capability to thwart Hitler's ambitions, you've got Night of the Long Knives, re-armament, the growing personal influence of Hitler over the Wehrmacht etc etc.