(A) The massive military buildup of all the European countries.
(B) Assassination of Adolf Hitler
(C) Assassination of Gravilo Princip
(D) ** The assassination of Archduke Franz Ferdinand
EXPLANATIONS BELOW
Concept note-1: -The assassination of Archduke Franz Ferdinand was the immediate cause of a war between two great powers-Russia and the Habsburg Austro-Hungarian Empire.
Concept note-2: -Two shots in Sarajevo ignited the fires of war and drew Europe toward World War I. Just hours after narrowly escaping an assassin’s bomb, Archduke Franz Ferdinand, the heir to Austro-Hungarian throne and his wife, the Duchess of Hohenberg, are killed by Gavrilo Princip.
Concept note-3: -When it was learned that the heir-apparent to the Austrian throne, Franz Ferdinand, was scheduled to visit Sarajevo in June of 1914, the Black Hand decided to assassinate him because of his perceived threat to Serbian independence.
Concept note-4: -The assassination of Austrian Archduke Franz Ferdinand (June 28, 1914) was the main catalyst for the start of the Great War (World War I).