Excerpts from Books and Wikipedia
"In 771 BC the Zhou house moved its capital from the Wei valley near Xi'an eastward to Luoyang, thus inaugurating the Eastern Zhou. Already Zhou power was being gradually diminished by the growth of many aristocratic family-states out of it central control. By the so-called Spring-and -Autumn period (722-481 BC) there were about 170 such states, each centered in its walled capital. These states formed alliances and leagues and engaged in diplomatic-military free-for-all, some absorbing others. By the era of Warring States (403-221 BC) only seven major states remained in the competition, most of them on the populous North China plain." [Fairbank: China, p. 49]
"The years between 481 and 403 were so confused that many historians, who divide the period when the Zhou occupied their eastern capital (the Eastern Zhou Period, 771–221) into two halves (the Spring and Autumn Period, 771–481, and the Warring States Period, 403–221), do not even try to give a name to the roil of years between the halves. It is a kind of interregnum." [Bauer: Ancient World, p. 497]