Parts 1 and 2 can be found here, and here
Thomas Aquinas on obeying the secular power
Eight hundred years ago, St. Thomas Aquinas weighed in on this question of legitimate state authority. He answered by examining the particular authority in question regarding both its origin and subsequent use (or abuse) of its power.
In his Commentary on the Sentences of Peter Lombard, St. Thomas did not view the “governing authorities” of Romans 13 as referring specifically to coercive governmental rulers, but to anyone who exercises authority over another. This could be a Church leader, an employer, or the emperor Nero. St. Thomas—speaking of Romans 13—wrote:
“Christians are bound to obey the authorities inasmuch as they are from God; and they are not bound to obey inasmuch as the authority is not from God.” Book 2, dist. 44, quest. 2
He continues by setting forth two ways by which an “authority may not be from God.” The authority is invalid from the outset if power was acquired by illegitimate means, such as by “violence, or simony or some other illegal method.” St. Thomas wrote:
“for whoever possesses himself of power by violence does not truly become lord or master. Therefore it is permissible, when occasion offers, for a person to reject such authority.” Id.
Even if the authority is accepted as legitimate in its origin, it does not mean that the authority is free to rule however it likes. In addition to declaring that a usurper had no claim to obedience, St. Thomas also taught that authority becomes illegitimate if the authority: 1) abuses its power or 2) goes beyond the purpose for which the authority is constituted. He gave as examples: an authority which commands a sinful action; or where the authority demands the property of another when nothing is justly owed.
“In keeping with the teachings of Jesus, the command to a sinful action always requires disobedience, while an unjust demand of payment might be obeyed or disobeyed.” Id.
What are kingdoms but great robberies?
St. Augustine, in the City of God, taught that an unjust government is no more than a criminal gang on a massive scale:

“Justice being taken away, then, what are kingdoms but great robberies? For what are robberies themselves, but little kingdoms? The band itself is made up of men; it is ruled by the authority of a prince, it is knit together by the pact of the confederacy; the booty is divided by the law agreed on. If, by the admittance of abandoned men, this evil increases to such a degree that it holds places, fixes abodes, takes possession of cities, and subdues peoples, it assumes the more plainly the name of a kingdom, because the reality is now manifestly conferred on it, not by the removal of covetousness, but by the addition of impunity.
“Indeed, that was an apt and true reply which was given to Alexander the Great by a pirate who had been seized. For when that king had asked the man what he meant by keeping hostile possession of the sea, he answered with bold pride, What you mean by seizing the whole earth; but because I do it with a petty ship, I am called a robber, while you who does it with a great fleet are styled emperor.” Book IV, Chapter 4.
Despite the general rule to obey the government, these early Church fathers make it clear that such obedience is conditional. In the next post, we will examine the duty to honor and respect the ruler. We will consider historical evidence suggesting that St. Paul’s own respect for the authorities was conditional and no better than the ruler deserved.