The brokenness of feudal government
Obviously, from the title alone, even just from the single word "Tyrant" the novel appears to be dealing with government brokenness. This time, it's the feudalism of early Spanish colonies in Central America. Instead of falling into social harmony and order, feudalism opens a door for powerful, exploitative people to dominate entire cities and towns, simply by occupying the castle and by imposing harsh rule. The feudal brokenness of the book is not some purposeless reference to history. Rather, it's a picture of all human injustice, because it shows what motivates people to mistreat others: the temptations of power and wealth.
Harmony versus injustice
Instead of understanding justice in its moralistic terms, words like right and wrong, this novel seems to understand justice as a matter of social harmony. Perhaps, it is best for the people that there be a ruler above them, but the specific tyrant in question saw power and profit as a thing to be seized and taken advantage of, so instead of falling into a harmonious balance, the king made an enemy of his own people. Injustice is portrayed as the lack of balance in the scales between the government and the people.
Exploitation versus respect
If the people are angry about exploitation (they are), then what it is exactly that they would want? Well, it seems from their behavior that they feel their lives are worth equal respect to the king's, which would be a good reason to stop exploiting them. If the king were subject to some kind of divine law that rendered all the humans to be essentially equal, then he would not be able to exploit others without incurring judgment (in their own religious terms). But the king views himself as if he is of greater importance, just because he has the initiative to seize power. He has no respect for their lives or their souls—nothing. He is a solipsist and a narcissist.
