The main thesis of my dissertation is that Kant has a just war theory, and it is universal just war theory, not a traditional just war theory. This is supported by first establishing the history of secular just war theory, specifically through a consideration of the work of Hugo Grotius, Rights of War and Peace. I take his approach, from a natural law perspective, as indicative of the just war theory tradition. I also offer a brief critique of this tradition, suggesting some issues that are endemic to these kinds of theories. From this general understanding, the version of Kant’s just war theory present in Brian Orend’s work War and International Justice: A Kantian Perspective, is explored and rejected as another traditional just war theory. Orend attempts to shoehorn Kant into a tradition which Kant rejects as ineffective, and poorly grounded. Orend’s work is not without merit, and his view is reconceptualized in the last chapter. If not a traditional just war theory, then either a new category of just war theory needs to be established, or the thesis ought to be rejected. Thus, the next task is to defend against the claim that Kant does not have a just war theory at all, as claimed by Howard Williams in his work Kant and the End of War. This is rejected as insufficiently nuanced in its interpretation of Kant, and also for resulting in principles contrary to Kant’s moral theory. This view is also utilized in a new manner in the last chapter. Prior to describing the new category of just war theory, I consider the general approach Kant had to war. To do this, I explore his philosophical approach on ever more specific areas of philosophical investigation. I conclude that Kant has a dynamic and progressive understanding of the concepts he investigated, including philosophy, humanity, ethics, politics, and, eventually, war. In the penultimate chapter, I establish what I call a universal just war theory. I consider and name the traits of both a traditional just war theory and a universal just war theory, using Marxist Communism as an explanatory example of universal just war theory. This provides an intellectual space for Kant’s theory to reside, which is also consistent with his philosophical approach. The last chapter is devoted to the explanation and application of Kant’s universal just war theory. I offer an overarching principle for Kant’ view of conflict and defend it as a universal just war theory. I also revisit the place Orend and Williams views’ have in a proper understanding of Kant on just war. I end with an application of Kant’s universal just war theory to previous conflicts, as a demonstration of the practical value of this view. Thus, through first a negative argument against current conceptions of Kant’s views of just war theory, and then a positive argument for Kant’s general philosophical approach and a new category of just war theory, I offer an interpretation of Kant on just war theory. I argue this interpretation is superior to previous ones, and recommends real world applications for just war theorists to utilize.