The two civil wars from 1642 to 1648 proved to be calamitous for the cause of divine right monarchy in England. Filmer's greatest fears about the parliamentary radicalism in the mixed regime theories of Hunton and Parker, the latter eventually becoming a secretary of state under Cromwell, were realized in the regicide and the establishment of the Commonwealth in 1649. Filmer lived to see not only the triumph of Calvinist and Independent resisters over crown and church, but also the utter implosion of Charles and the moderate royalists' argument for mixed monarchy when a radicalized Parliament assumed the full right of sovereignty as the sole representative of the nation. The postwar period also, however, saw the publication in 1652 of the nothing if not resilient Filmer's Observations concerning the Originall of Government, the greatest portion of which composed an extended critique of Hugo Grotius' De Jure Belli ac Pacis and Thomas Hobbes' Leviathan. With this substantial offering in the closing years of his life, Filmer's work took on a somewhat new direction. Whereas his prior efforts had focused primarily on the Catholic natural law and the Calvinist-influenced parliamentary resisters, now near the end of his career Filmer trained his sights on the two most prominent natural law and natural rights theorists of the period.

Unlike his Catholic and Calvinist theological opponents of years past, Filmer's new antagonists in the natural liberty school did not fuse their arguments for consent with the principle of divine ordination of political power.