Reason for war declarations with Germany on Russia ww1

The Serbian Expansion and Russian role in the Balkans.

Combined with the increase in Russian military strength, both Austria and Germany felt threatened by Serbian expansion; when Austria invaded Serbia on 28 July 1914, Russian Foreign Minister Sergey Sazonov viewed it as an Austro-German conspiracy to end Russian influence in the Balkans.

On 30 July, Russia declared general mobilization in support of Serbia; on 1 August, Germany declared war on Russia, followed by Austria-Hungary on 6th.