-Austria-Hungary backed by their ally Germany told Serbia to begin an investigation into the assassination and take steps to eliminate all nationalist, anti-Imperialist groups. -The ultimatum was served to Serbia on July 23rd 1914 and they were given 48 hours to decide whether or not to accept the terms. -Serbia immediately appealed to their ally, Russia, for support. Russia began to mobilise its troops in preparation for potential war against Austria-Hungary