Hellanikos, Thukydides and the era of Kimon

The first historian to record the period from the Persian Wars to 431 BC was Hellanikos, the author of a now lost History of Anthens from its mythical origins through the fifth century BC. According to Hellanikos, there was one war between Athens and Sparta from 431 to 421 and another from 412 to 404, and the first of these two wars was the outcome of events which took place in the 430s.
THukydides, writing a monograph on a war he sought to establish as the most disastrous to date, criticised Hellanikos as chronologically inaccurate and lacking an appreciation of the impact of a stronger Athens. Thukydides asserted that there was only one war, beginning in 431 and ending in 404. It cause was the growth of Athens following the Persian Wars, and the fear which that growth inspired in Sparta.