Although the German leaders were aware of the domino effect of attacking Serbia, they supported Austria.Since Germany and Austria wanted a quick attack on Serbia, so that other countries would not get involved, an ultimatum was sent. When the ultimatum was sent to Serbia in July 23, 1914, which demanded Serbia to abolish all anti-Austrian activities and allow Austria to investigate the assassination of Francis Ferdinand. Serbia accepted to the ultimatum but did not allow Austria to investigate the murder. This caused Austria to declare war on Serbia on July 28.When Austria attacked Serbia, as the German leaders had anticipated, Russia prepared to attack Austria. Germany warned Russia to stop the preparation, but because Russia did not listen, Germany attacked Russia on August 1. Two days later, Germany also declared war against France, which was Russias ally.Germany planned to invade France through Belgium, but unfortunately, Belgium refused this. On August 3, Germany invaded Belgium. The British then became involved in the war, for they had promised Belgium could be neutral, and not get involved in wars.1 In addition, the British had to join the war because if they did not, Germany would control the continent of Europe. In less than six weeks, the domino effect had caused Serbia, Russia, France, Belgium, and Britain to fight against Germany and Austria-Hungary.The WW1 finally broke out in June 1914 because of an accident in Bosnia. It was the Sarajevo incident, the immediate cause of WW1. It took place on June 28, 1914. On that day, Archduke Francis Ferdinand, heir to the Austrian throne, and his wife were shot dead by a young Serbian student at Sarajevo, the Bosnian capital. Austria considered the murder of the heir to the throne an open Serbian attack.2 Austria would be left without an heir. Although she could not find any evidence that the Serbian government was connected with the assassination.