Which was the cause of world 1?
A) Europe’s system of military alliance’s enlarged in small conflict
B) Political revolutions in Europe left nations unstable
C) the second industrial revolution led to international rivalries
D) Russia’s race to industrialize threatened the economy of other European countries

The immediate cause of World War I that made the aforementioned items come into play (alliances, imperialism, militarism, nationalism) was the assassination of Archduke Franz Ferdinand of Austria-Hungary. In June 1914, a Serbian-nationalist terrorist group called the Black Hand sent groups to assassinate the Archduke.

ANSWER--->  So the answer would in fact be, B (Political revolutions in Europe left nations unstable.)

I HOPE THIS HELPS YOU OUT! ALSO, PLSSS MARK ME AS THE BRAINIEST.

 I think it's establishment.

Explanation:   :)