You do not need extensive knowledge of history to study political philosophy. Political philosophy in essence is a field of applied ethics: that is, it applies morality to a political entity. So what is needed is the basic, normative theories of ethics (e.g., utilitarianism and duty ethics). Some popular topics of political philosophy presently are these:
- The nature of political power: is it good, bad, or value-neutral?
- The source of the govt authority: is it through social contract, brute force or great consequences?
- Political obligation: Is there a duty to obey all laws or some laws or no such a duty at all?
- Democracy: If democracy is legitimate, on what moral grounds does the legitimacy stand?
- The goal of governing: is it for the sake of the good life of the people, or is it for the embodiment of justice without judging or enforcing a conception of the good life?
Authors of political philosophy use historical events to motivate readers. Rawls, e.g., used the war of religion (the 16th century inquisition) to illustrate why a liberal society which encourages individuals to form and experiment their own conceptions of good life can be inherently unstable. Rawls believes that sooner or later people will try to impose their own conceptions of the good life onto others. John Stuart Mill used the British Corn Laws of 19th century to explain when the right to free speech can be fully exercised and when it can be abridged. So historical knowledge helps to understand authors' point, but you can easily google historical events. So history is not a prerequisite, unlike the knowledge of ethics.