The first type of argument Kant gives for the second definitive article concerns state of nature theory. Initially Kant presents states as akin to individuals and points out that in a state of nature they wrong each other merely by being contiguous with each other. The very fact that states are in close relation with each other produces a condition that is wrong so that each should, for the sake of their own security, enter with each other into a civil constitution analogous to that which led to the formation of states in the first place. This comparison of the relation of states between each other to the state of nature that existed prior to the formation of states in the first place is one that should carry with it, if the analogy was perfect, an argument for a world state.
Kant does not regard the argument as perfect, however, as he shows by going on to argue that what the analogy with the state of nature points to is not a "state of nations" but only a "league of nations". The first reason given for avoiding the formation of a general world state is odd since Kant simply refers back to the operation of sovereignty within any given state and then says that if we had a world state we would no longer have separate operative nations but only one. However this is hardly a ground in itself since surely we have found a reason for thinking that it would be better for there to be one state than many?
Not only does Kant's first rationale for suggesting that we require a league of nations rather than a "state" (of nations!) beg the question but the subsequent discussion suggests a further ground for thinking that the formation of a general state is preferable to the existing condition. Reverting to the comparison with the state of nature Kant points to the difference between "mad freedom" and "rational freedom" and asserts the difference to be one between a form of "freedom" that authorizes savage behaviour to one that enables a civilized condition to come into being. The problem with overcoming such a state of nature, when it comes to states, is said to reside in the commitment of heads of state to behaving in typically despotic fashion by putting their peoples at risk for matters that don't really concern them. A comparison between Europeans and American Indians is then vouched in which the former are seen to be "superior" to the latter only in terms of having an instrumental response to people that enables the multiplication of them for more wars!
Similarly, Kant points to the use made by states of legal writings of thinkers such as Grotius and and Pufendorf, to support a right to offensive war, whilst no state has ever been dissuaded from going to war by considering arguments from such sources. The behaviour of states towards each in the state of nature between is in fact evidence of the "malevolence of human nature" (Ak 8: 355). Given all this one would expect some argument to now be forthcoming for why it is that we cannot over-ride the distinction between states and form one state.
At this point Kant states that the way in which states pursue right in relation to each other can be only by means of war since there is no court between them. This shows, as he re-states, a reason why states should leave their present condition. This requires a pact of nations among themselves to create a pacific league aimed at ending war forever. Now, Kant returns to the question of why this league should not be a new world state and gives what is in effect his second argument for a federal union rather than the formation of a world state. This second argument states that the league is to be formed not for the purposes of acquiring power but only to preserve and secure the freedom of states in their league with each other. So this time Kant does not simply beg the question but suggests that the motivation towards the league within each state is towards the protection of the freedom that each has attained independently.
This second argument, however, also points back to the first definitive article since it is pointed out that the reason for hope that such a federal union could be formed is grounded on the inclination towards peace of republics once they are formed. It is the possession of republican constitutions that will lead states to union with each other in order to "secure a condition of freedom of states conformably with the idea of the right of nations" (Ak. 8: 356). So the suggestion is that once republics exist they will, by incarnation of the principles of right internally to each one, naturally attract towards each other and that this natural attraction will act as a basis for the inclination towards peace.
The federal union is nonetheless still presented by Kant as a "surrogate" of the civil union that any given state represents. The discussion of the second article concludes with revisiting the comparison with the state of nature and now Kant indicates that superseding the state of nature between states does point to the formation of the state of nations that his first argument apparently ruled out! In conclusion he points out that the problem with the formation of such a "state of nations" is that separate states, in accordance with the idea of the right of nations, do not wish to form such a state. So the states themselves reject the hypothesis of such a state even though Kant now concedes that such a state is a correct thesis. Hence, his third "argument" is simply that we place the negative idea of a league that averts war in place of the positive one of a world republic simply because individual states are likely to be more receptive to the former idea than the latter one.
The third "argument" appears the weakest of the three but perhaps it is, instead, the strongest. The attention to the existent views of states was also mentioned in the discussion of the division of the preliminary articles where settled opinions were invoked in terms of why previous inheritances of states could continue to be allowed despite the fact that such inheritances were not really in accord with right. Similarly, here Kant appears to be concluding that we should accept the division between states since states themselves appear to have a settled insistence on it. That would indicate that such acceptance is something provisional that we might hope to overcome by means of the federal union and make Kant's grounds for preferring the negative league to the positive republic similar to his invocation of the general public opinion in the division of the preliminary articles. However, to accept this as a good ground would require revising my earlier treatment of the invocation of public opinion in the division of the preliminary articles and indicates further the need to think through the normative status of such a reference in Kant's thinking. It will need to have something to do with publicity and suggests a connection in some sense between public opinion and the concluding invocation in Perpetual Peace of the principles of publicity.