What was the reason for Germany’s declaration of war on Russia?

The reason for this was that Austria then accused the Serbs of the murder of Franz Ferdinand. Austria was supported by Prussia, and Russia stood up for the Serbs. Thus, Germany on August 1 declared war on her. So in the summer of 1914, a world war was unleashed. The war itself had rather unpredictable outcomes for the countries that started it. So most empires collapsed after its completion. For example, Austria-Hungary completely disintegrated.