The clause in the constitution which subjected its framers to the bitterest criticism at the hands of anti-slavery agitators is that which requires that a "person held to service"--the term "slave" is here avoided also--in one State and escaping to another shall be delivered up on claim of the party to whom the service is due. In view of the interests to be reconciled this clause was undoubtedly necessary to union.[163] If the free States were to become a place of refuge for escaping slaves it meant disaster for the States in which the institution of slavery existed and they insisted upon this as a self-protective measure. The constitution recognized the right of each State to preserve the integrity of its own domestic institutions. "It can never too often be called to mind," says Rhodes, "that the political parties of the Northern States and their senators and representatives in Congress, scrupulously respected the constitutional protection given to the peculiar institution of the South, until, by her own act, secession dissolved the bonds of union."[164] The tragedy of the situation lay in the fact that the political necessities of the time made unavoidable this strange union between freedom and slavery, the fundamental incompatibility of which the expanding national life was bound to make clear to the minds of men. Looking back on this momentous period we are struck with what Lecky calls "the grotesque absurdity of slaveowners signing a Declaration of Independence which asserted the inalienable right of every man to liberty and equality."[165] That the contradiction existed, that it was felt by men like Jefferson, and that it was destined to become more prominent in the mind of the nation as the implications and applications of the great ideas of freedom and equality were enriched and enlarged in the expanding life of a virile democracy, can not be denied. But it may be remarked in the defense of our Revolutionary fathers that they were facing the practical problem of effecting national unity and that "it is a tendency of the Anglo-Saxon race to take the expedient in politics when the absolute right can not be had."[166] They compromised on slavery and on the whole wisely. Moreover, the history of the development of great moral and political concepts indicates that men often formulate principles the logical implications of which are not grasped until new problems and the demand for new social adjustments emerge. The great moral categories of courage, temperance and justice first received scientific formulation at the hands of the Greeks; the ever swelling stream of human civilization has vastly enriched and enlarged these conceptions but without altering their essential meaning. When the idea of liberty which in 1776 included only one class, namely, those who owned the property and administered the government of the nation, was expanded so as to include every member of the social order, at that moment slavery was doomed.