a) Sarajevo crisis: On June 28, 1914 Archduke Ferdinand along his wife Sophia were assassinated by a student of the ‘Black hand’, a revolutionary organisation, at Sarajevo, the Capital of Serbia.
Austria served an ultimatum on Serbia on July 23 making eleven demands. Serbia accepted most of the demands except those that would have led to the loss of her sovereignty. Austria declared war on Serbia on 28th July 1914. This was the immediate cause of the Fist World War.
b) The involvement of the five major powers in the hostilities were Germany, Austria-Hungary, France, England and Russia.
c) The Hapsburg dynasty in Austria-Hungary was destroyed. Austria and Hungary became separate independent states. Austria was made to sign the treaty of Saint-Germain-en-Laye on 10th September 1919. The treaty declared that the Austro-Hungarian Empire was to be dissolved. Austria recognised the independence of Hungary, Czechoslovakia, Poland and the Kingdom of Serbs, Croats and Slovenes. The treaty included 'war reparations' of large sums of money, directed towards the Allies. Hungary had to sign the Treaty of Trianon. Hungary lost a lot of its lands to neighbouring countries such as Romania, Yugoslavia and Czechoslovakia. Hungary was partitioned, lost two thirds of her territory, and lost one third of her Hungarian population.