The progression of Revolutionary thought in the 17th century, Part 1

I have lately undertaken to read Algernon Sidney on government. ... As often as I have read it, and fumbled it over, it now excites fresh admiration [i.e., wonder] that this work has excited so little interest in the literary world. As splendid an edition of it as the art of printing can produce—as well for the intrinsic merit of the work, as for the proof it brings of the bitter sufferings of the advocates of liberty from that time to this, and to show the slow progress of moral, philosophical, and political illumination in the world—ought to be now published in America.
John Adams to  Thomas Jefferson in 1823.

Algernon Sidney (or Sydney in England) was one of the leading theorist in the Republican movement in 17th century England. (Note: This Republican movement or "Republicanism" which was a "Laisse Faire" and "Natural Right" movement has nothing to do with the Republican party in today's U.S. politics, which more closely resembles corporate fascism).
Sidney's importance was more or less his stress on the Right to Revolution, and his death was seen as kind of a martyrdom in the Republican/Libertarian movement, as he was beheaded by King Charles ll, and his "Discourse Concerning Government" was actually used against him in court, as witness against him.
To Sidney, revolution and freedom were the Right, and Duty of an oppressed people.
"Revolution to Sidney was not an evil but the people's great weapon for the overthrow of Tyranny and for exercising their Right to popular government. There was nothing sacred about governments, which on the contrary should be changed as required." (Murray Rothbard's "Conceived in Liberty" Volume 2, chapter 33)

Sidney championed law as "written reason" and as defense of Life, Liberty, and Property: " If there be no other law in a kingdom than the will of a Prince, there is no such thing as Liberty; and 'tis impossible for a man to have a Right to lands and goods, if he have no Liberty, and enjoys his life at the pleasure of another, as it is to enjoy either when he is deprived of them."
Sidney believed that government basically had an agreement or contract with the governed, and if the government failed in its duties, it simply needed to be removed. He also believed the People could not be made to give up their freedom, nor could they be bound to the government by dead hands of the past.
When he was being led to execution, in his "Dying speech" he said, "God has left nations the Liberty of setting up governments as best please them."
Injustice, to Sidney, made a government illegal. "Swords were given to men that none be slaves, but such as knew not how to use them."
In conclusion to part 1, I will leave with this from Sidney," Let the danger be never so great, there is a possibility of safety whilst men have life, hands, arms, and courage to use them, but the people must certainly perish, who tamely suffer themselves to be oppressed, by the injustice, cruelty, and malice of an ill magistrate."

For more on Algernon Sidney, read Rothbard's "Conceived in Liberty."