Who did a Serbian terrorist assassinate?

When Austria-Hungary declared war on Serbia, Who promised to support Austria-Hungary?

Who promised to support Serbia?

Who declared war on Russia

To support her ally, Russia, Which country began mobbing their armies against Germany?

Germany needed to defeat France quickly, before she could take on Russia's massive army. To invade France more quickly, who did the army go through?

Who promised to help Belgium if she was attacked