How did assassination of archduke franz ferdinand lead to start of world war?

Explanation:  The assassination of Franz Ferdinand in Sarajevo on June 28, 1914, was the long-awaited cause for declaring war on Serbia, due to decades of tensions between Austria and Serbia. The reasons for these tensions were the imperialist intentions of Austria and the aspiration to further expand influence on Balkans on the one hand, and nationalist aspirations of Slavs to create independent nation states on the other.   After the assassination of Ferdinand and his wife in Sarajevo, Austria sought help from Germany, received a famous blank check and declared war on Serbia. Later, Russia entered to war on the side of Serbia, then great powers against Germany and Austria Hungary, and thus the World War arose.