Thucydides (c. 460 B.C. - c. 395 B.C.) was a Greek historian and author of the History of the Peloponnesian War. Thucydides is considered the father of "scientific history," because of his strict standards of evidence-gathering and analysis in terms of cause and effect without reference to the intervention of the gods. The History of the Peloponnesian War is the history of the 5th century B.C. struggle between Athens, a democratic state and sea power, and the states of the Peloponnese headed by Sparta, a conservative power with an efficient military force.