Though I've just spent a fair bit of time attempting to demonstrate that the Declaration is in many ways a conservative document, it certainly does contain some very important radical elements. In fact it’s these elements that have arguably kept the Declaration relevant almost 250 years after it was written, and changed the way that people across the world think about government and it purpose. Having said that, I think it’s important to understand exactly what some of these radical elements are, what they mean, and where they came from.
In many ways the Declaration is predicated on the idea that all sovereign peoples have the right to overthrow any government which they feel has become destructive or abusive of their rights. Indeed, without this “right of revolution” the Declaration itself wouldn't make much sense. However, the idea that a people possess the ability to “dissolve the Political Bands which have connected them with another, and to assume among the Powers of the Earth, the separate and equal Station to which the Laws of Nature and Nature’s God entitle them” was not, in 1776, unique. Though Jefferson’s use of it as a justification for an ongoing rebellion were certainly novel, the right of revolution was actually a staple of 18th century Enlightenment (and particularly English) philosophy.
Specifically, the right of a people to revolt when treated unjustly by their government was first articulated by philosopher John Locke in his 1689 publication, Two Treatises on Government. Locke wrote these treatises during a period in his life when his was in exile from England because of his opposition to the Catholic, absolutist King of England, James II. They weren't published, however, until after the Glorious Revolution of 1688, which deposed James and installed in his place his daughter Mary and her husband William (who also happened to be a Dutch Prince, but that’s not important). Indeed, Locke claimed in the preface that he wanted to justify William’s ascension to the throne.
In the first of his treatises Locke described something called the “social contract” which he and other Enlightenment thinkers believed was basis of all states and governments throughout human history. In nature, Locke wrote, man enjoys complete freedom, but very little security. As a result, people tend to band together and form communities, to the mutual benefit of all (in theory). The unspoken social contract between people in these communities is that the common good, or common welfare, is the highest consideration. Because people enter into a social contract voluntarily for the purpose of protecting themselves and the things they possess, Locke claimed that they all retain a basic right to life, liberty, and property. When a government violates these rights, Locke described in his second treatise, it is guilty of violating the social contract. The people therefore have a right, and at times an obligation, to overthrow any government that is acting against the interests of the majority of its citizens and replace it with one that better serves their welfare.
These were, in 1689, very radical notions indeed. And while it is almost certainly true that Locke developed them before the Glorious Revolution took place, because his Two Treatises weren't published until after all was said and done it’s doubtful that the ideas they promoted were on the minds any of the revolutionaries in 1688 (at least not in a coherent form). Therefore the relationship between Locke, his theories and the revolution they were supposed to be justifying was largely academic. Like a scientist, Locke gathered his data (in this case from the political history of Western Europe), formed a hypothesis (the social contract), and having observed a particular event (the Glorious Revolution), had his hypothesis confirmed and published the results. Locke did not take part in the revolution himself, or significantly influence it, but merely anticipated it and commented on it.
Thomas Jefferson, on the other hand, was very much in the thick of his revolution. And since he was a man familiar with Enlightenment philosophy, and Locke in particular, it should come as no surprise that he saw in the situation he and his fellow colonists were facing almost exactly the scenario that Locke had described. When asked, along with some of his colleagues, to draft a justification for independence he invoked Locke’s right of revolution, putting into practice something that had previously existed only in theory. Specifically he wrote, after asserting that all men possess certain rights, that, “To secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness.”
By invoking the principles laid out by John Locke almost a century earlier, Jefferson not only provided what was to many observers a backwater colonial tax revolt with a robust philosophical grounding, but he also popularized what had been until then a relatively obscure philosophical theory. This effectively instilled in the population of the newly-formed United States of America the belief that any government that did not serve their needs or attempted to restrict their freedoms was illegitimate. While Jefferson would no doubt have applauded the people’s increased vigilance, this state of affairs became problematic during the early history of the American republic (when the Constitution was young and untested), and has arguably remained a force in the American political consciousness to the present day.