It is interesting to speculate on how Milton himself intended, or perhaps unconsciously attempted, to represent the very human events of his own century by means of the divine cosmic drama of Paradise Lost. Who would Satan be a metaphor for, in this case? Satan is a usurper, a rebel thinking to challenge the supremacy of God and carrying out a rebellion which God, though omnipotent and omniscient, has foreknowledge of, but does not preordain.
There is no conceivable way, in my view, that this literalist interpretation of the Judeo-Christian creation story can be matched with the events and figures of the seventeenth century. Though writers and commentators have retrospectively granted Satan the status of "hero" in the poem, these are cases of presentism: the attribution of the attitudes of one's own time to past writers or to people in general who lived in earlier periods. Shelley and Blake admired the character of Milton's Satan because they were anti-religious rebels themselves. There is no evidence that Milton himself felt this way or even, in my view, that he subconsciously made Satan to be the supposedly admirable character Blake, Shelley, and others have thought him.
If, however, Milton had actually had such thoughts or intentions, the most obvious analogy would be one between Satan's war against God and the English Civil War, in which the king was deposed and executed. But Milton, of course, was on the side of Parliament and the Commonwealth and against the monarchy. There was indeed a crisis of authority in England that affected every aspect of Milton's mature life, but it was one in which Milton was on the anti-authoritarian side. This is consistent with seeing Paradise Lost as an allegory of England only by judging Milton as having deliberately made Satan the hero which, I believe, is false.
The alternative is to imagine that Milton somehow intended God to represent Cromwell and the Commonwealth and Satan as a stand-in for the English monarchy that had corrupted the people and illegitimately claimed authority over them. This is an intriguing interpretation, I admit, but I don't think it's a realistic one. Milton, granted his flaws, was a genuinely devout man who wished to enshrine in his art what he believed to be the eternal truths of God and God's relation to man. He saw the struggle against the "tyranny" of Charles I as a corollary of his religious beliefs, and, no doubt, the religious fervor of the cause encouraged him to write such a monumental epic (which he did after the cause had been defeated and the Restoration had taken place). But I doubt that the anti-authoritarian Satan was intended by Milton as a symbol of anti-authoritarian human actions in the England of the 1600s. And I doubt as well that he (conversely) intended to equate God's infinite authority with Cromwell and Parliament. Anything, I suppose, is possible, but one has to read a lot of extraneous thinking into Paradise Lost in order to interpret it this way—or overinterpret it, I would think.
Perhaps the most important “crisis of authority” in England in the seventeenth century was the rebellion against King Charles I and his execution as part of the English Civil War. Milton was a strong proponent of revolution and held a key position in the revolutionary government. He justified the execution of the king, whom he considered a tyrant rather than a legitimate, godly ruler. Charles, by ruling in ungodly ways, had provoked the “crisis of authority” that led to his execution. This, at least, was certainly Milton’s view.
Milton’s earthly, political republicanism might seem to conflict with the enthusiastic support he shows for divine kingship in Paradise Lost. The same person who opposed tyranny on earth had no trouble justifying the ways of God to man in Paradise Lost. This was because God, by definition, was not a tyrant but a king who was essentially goodness personified.
The character in Paradise Lost who most resembles Charles I is Satan. Satan is unscrupulous, dishonest, driven by pride, and in revolt against God – all traits that Milton also associated with Charles. Although defeated on the battlefield, as Charles had been, Satan refuses to submit (as Charles had also done):
. . . What though the field be lost?
All is not lost; the unconquerable will,
And study of revenge, immortal hate,
And courage never to submit of yield:
And what is else not to be overcome?
Rather than showing any regret or repentance or humility for rebelling against God and goodness, Satan is defiant – just as Charles (in Milton’s opinion) had also been. Charles, in Milton’s view, had ruled over a court that was corrupt, self-indulgent, superficial, materialistic, and selfish. Charles, again in Milton’s view, had lied to people and had misled them. He had tried to use propaganda to prop up his own power, and he had been more concerned with shows of virtue than with the functioning as a truly good king. In all these ways he resembled Satan.
Above all, Charles (in Milton’s view) had been motivated by pride and selfishness and showed little real concern for the beings who depended on him to think and act wisely.
Therefore, Paradise Lost celebrates the righteous authority of God while condemning the evil tyranny of Satan.