When discussing the second definitive article Kant arguably gave no clear reason why there should not be a world state. Now, Kant responds to the problem of why states should remain independent of each other, given that this involves a state of war between states, by discussing a specific danger that arises from overcoming such a condition. This is that fusion of states together into one larger state could simply arise from one state overpowering the others and turning into a universal state by this means. However, in discussing this possibility, Kant argues that such a universal "monarchy" (as he terms it) leads to a specific problem. This is that as laws gain in range they decline in vigour. In other words, as a state expands its range of operation it becomes more difficult for the laws in question to be based on a general agreement and to capture true consent. This argument is similar to the ones used by Rousseau to argue for smaller polities (and there is precedent for it also in Plato) but is not one that arises from concern with the specificities of international right. Nor is it the case that such an argument applies to a world state that has arisen from federative unions moving by their own momentum towards a general universal state.
That Kant's concern here is primarily with conquest is made further clear when he goes on to talk of every head of state having the ambition of creating peace by means of becoming the ruler of the world. In response to this danger Kant makes his second appeal to the means of nature. Now he refers to how the ambition of heads of state to create a universal monarchy by means of conquest is undercut by two central differences within the human race. These are differences of language and religion (though Kant here inserts a note to the effect that the latter are not really differences of rational religion but of dogmatic creeds). These differences promote many bases for war between peoples thus creating an obstacle to the ambition of heads of states. However, despite making the appeal to "nature" on these grounds, Kant goes on to point out that increase of culture leads to an agreement on principles by promoting a kind of equilibrium between them (shades here perhaps of Rawls' notion of "overlapping consensus"?).
Not only does this general agreement in principles itself undermine the differences Kant points to as undercutting the ambition of heads of states but there is a further uniting factor that is mentioned now. This is what Kant terms the "spirit of commerce" (Ak. 8: 368). The point Kant makes about this is that it cannot well coexist with war and that the power of money may be the most reliable of all powers for the promotion of peace. This argument in a sense follows from the earlier argument concerning the right of the state since there we found Kant appealing to the need for security of holdings (property) as a natural ground for the formation of the state. Similarly, the need for security of trade between partners in different nations grounds a basis for resistance to war amongst traders. The need for such security of trade promotes mediation between warring partners just as if there existed a permanent league to promote peace. So there is a virtual league that emerges automatically from the relations between states which may partially explain Kant's more sanguine attitude to the formation of a world state. It does however also point us back, in a sense not clearly undertaken anywhere directly by Kant, to the need to think further about the conditions for just and fair trade, a point discussed in previous postings.