Three weeks after the assassination in Sarejevo, Austria-Hungary had delivered an ultimatum upon the Serbian government. A reply could only be made on the following day, as th
…e Prime Minister was conducting an election campaign tour. The Serbian government had agreed upon most of the demands except for one; the Annexation of Several Serbian provinces to compensate for the events in Sarejevo and the continued propaganda against the A-H monarchy. Serbia had agreed to trial those commanding officers suspected of their involvement in the assassination, tighten weapon smuggling laws and precautions, limit propaganda against the Austria-Hungarian monarchy and for the trials to be conducted in Austria. BUT, it was seen against the Serbian constitution for the Serbian government to allow annexation of Serbian land. As the A-H government was depending on the rejection of the ultimatum, attack was promptly launched on the state of Serbia. Following this vicious and vengeful attack against Serbia, Russia has seen this as an oppressive attack directly on the Slavic faith and tradition. Following Austria-Hungary's attack on Serbia, Russia had seen this as a direct attack on common cultural elements and the Slavic, religion. Therefore, had declared war on Austria-Hungary. The fact that Germany had promised full support for A-H's attack on Serbia, it was also obliged to protect Austria-Hungary against any attack from Russia. At this point, Germany must promptly mobilize German troops into France, to reach Russia before it has mobilized enough troops. The Schlieffen plan stated that France must be defeated before any attack can be launched on Russia. Russia's faster than expected mobilization had foiled any attempt to invade France in time. To mobilize German troops into France, they must firstly march through Belgium. Under the treaty of London (aka The First Treaty of London) was signed on the 19th of April, 1839. Which signified Belgium's neutrality and protection from any German speaking state. Due to the Schlieffen plan, Germany's mobilization through Belgium had put the Treaty into affect, and Britain must now become involved in the conflict of the major European powers. Simply, under the alliance system, the assassination had eventually pulled all major European powers into conflict under several alliances. (MORE) 
