The concept that no man can be ruled without his prior consent.
Society is built on a series of laws and understandings; no man can be governed unless he deems those in power worthy of his respect, or capable of upholding his interests. This, in essence, is government by consent. Followers of this theory think rulers should never have the right to force any beliefs on those they rule. If the rulers don't have the consent of the masses they can be overthrown and replaced by others chosen by the masses.
Historically, philosopher John Locke spent many years musing about government, and the correct way to govern a society in order to preserve the rights of the individual. His thoughts culminated in his work "The two treaties of government." Each of these outlined his thoughts on traditional forms of government, and his suggestions on how things could be improved.
One of the earlier philosophy technologies, Government by Consent can pay dividends for a research-heavy faction due to its increase in research rate and its unlocking of further similarly beneficial technologies.