What is the forbade union with Austria?

The forbidding of a union with Austria refers to the prohibition against the unification of Germany and Austria, primarily established by the Treaty of Versailles and later reinforced by the Treaty of Saint-Germain after World War I. This was part of the Allied powers' efforts to prevent the resurgence of a powerful German Empire that could threaten European stability. The principle of self-determination and the desire to maintain a balance of power in Europe were also key factors. Ultimately, this prohibition was a significant factor in the political dynamics leading up to World War II.