How did Germany first get involved in World War 1?

On June 28, 1914, Archduke Franz Ferdinand of Austria was assassinated by a Serbian nationalist in Sarajevo, the provincial capital of Bosnia-Herzegovina (formally annexed by Austria-Hungary in 1908). In response, Austria-Hungary issued an ultimatum to Serbia that was deliberately designed to be unacceptable. When Serbia failed to comply with all of the ultimatum's terms, Austria-Hungary declared war on July 28, 1914.

As a result of its alliance with Austria-Hungary, Germany was now obligated to come to its aid. On August 1, Germany declared war on Russia, which had mobilized its army in support of Serbia. Two days later, Germany declared war on France, Russia's ally.