Why was the alliance system in pre‒World War I Europe both a blessin

Why was the alliance system in pre‒World War I Europe both a blessing and a curse?

A) If successful, Europe would boom economically, but if not, depression would result.
B) It could produce agricultural abundance or starvation.
C) It could both appoint and remove monarchs.
D) It could maintain peace or bring about war.

ANSWER
Answer: D