Thucydides Concluded That the Underlying Cause of the Peloponnesian War

Thucydides concluded that the underlying cause of the Peloponnesian War was

A) the clash between Athens's democratic society and Sparta's authoritarian government.
B) that Sparta was a sea power seeking new ports.
C) a changing distribution of power between Athens and Sparta.
D) Athenian leaders were pacifists and did not build their army.
E) Spartan culture led to constant war against more civilized city-states.