How did the assassination of archduke francis fernidad lead to world war 1

When the archduke was assassinated, Austria-Hungary declared war on Serbia after finding out that the government of Serbia was behind the assassination. However Russia was allied with the Serbs and declared war on Austria-Hungary. Since Germany was allied with AH and declared War on Russia and vise versa. France joined the war because France is allied with Russia. And after AH and Germany declare war on France, Britain joins the war because they are allies with France.