In ww1, why did Germany declare war on Russia?
Before the outbreak of the First World War, Germany, Austria-Hungary, and Italy signed a pact called the Triple Alliance. This alliance declared that if any member of this pact was attacked by a foreign power that the other countries would aid in their defense. After the assassination of Archduke Franz Ferdinand in Sarajevo, Serbia, Austria declared war on Serbia.
To protect their Serbian ally, Russia then declared war on Austria and began to mobilize their forces. In accordance with the Triple Alliance, Germany then declared war on Russia.