To prove this, let Facts be submitted to a candid world

Note the archaic use of "candid," in this case meaning "unbiased." To what does "this" refer? To the preceding lines, 16-19; but specifically, "this" refers to lines 19-20: "The History of the present King of Great-Britain is a History of repeated Injuries and Usurpations, all having in direct Object the Establishment of an absolute Tyranny over these States." That is, King George III ("the present King of Great-Britain) has repeatedly shown, in various ways to be enumerated in what follows in the text of the Declaration, that he intends to establish an absolute tyranny over "these States." Note that Jefferson does not refer to them as "colonies" but as "states." Note also the word "usurpation." To usurp is to seize or assume something wrongfully--in this case, political power. This should be kept in mind when reading the charges against the King. One should continually ask, Why was it wrong for King George to do this or that? Jefferson must demonstrate that King George has shown that he intends to establish a tyranny over the states to justify the assertion in the Preamble that it has now become necessary for the people of America to separate themselves from Great Britain. In each case, the grievance must show that the king's actions violate the unalienable rights of humanity, or the principle that government must be by consent, or both.