What led to German declaration of war against and russia?

Germany declared war on Russia on August 1, 1914, primarily due to the complex web of alliances and escalating tensions following the assassination of Archduke Franz Ferdinand of Austria. Russia mobilized its forces to support Serbia, a Slavic ally, which prompted Germany to view this as a direct threat to its own security. Germany had previously issued an ultimatum to Russia to halt its mobilization, and when Russia did not comply, Germany declared war to uphold its alliance with Austria-Hungary and to assert its military strategy. This declaration marked a significant escalation in the conflict that would lead to World War I.