When in the Course of human events it becomes necessary for one people 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 of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.
The Dependent Clause (in white) cannot stand on its own despite the presence of a subject (it) and a verb (becomes) because the thought is incomplete due to the conjunctive adverb (when).
The Dependent Clause (in white) cannot stand on its own despite the presence of a subject (it) and a verb (becomes) because the thought is incomplete due to the conjunctive adverb (when).