It is my intention in this letter to took into the causes which have led to the war in which we are now engaged with Mexico. I must premise, that we must take the world as we find it, and we must decide according to the ethicks and practice of the most civilized nations, and not according to standards of morality, which, although perfect in themselves, are inapplicable to the present imperfect state of mankind. It is again to be observed, that among nations, there is no common judge, to whom they are willing to submit their differences, and to obey the decision. Each is the judge in its own case, and if one should be disposed to do even more than justice, the demands of the other may be out of all reason. It is a rare thing in modern times, for two powerful civilized nations to be involved in hostilities, without previous differences, misunderstandings, or mutual aggressions, and without, also, previous unsuccessful attempts to adjust their differences in a peaceful way. Let us first consider the complaints of Mexico. These consisted, in the first instance, in the aid afforded by citizens of the United States in the struggle of Texas with Mexico for her independence. But this did not begin with that struggle, but with the efforts of Mexico herself to throw off the allegiance of Spain, in which she was so materially aided by the Americans of Texas, and who continued to be invited into that country for the purpose of giving strength to the Mexican cause. Serious offence was given to Spain in consequence of this volunteer aid of our citizens to her revolted provinces, but, certainly, there was no complaint on the part of those provinces. Their situation changed as soon as they won their independence, and when Texas revolted in consequence of alleged oppression, Mexico assumed the position before occupied by Spain, and complained of the aid afforded by citizens of the United States to Texas. Here is, no doubt, the ground of the ill-feeling on the part of Mexico towards us. How far we are responsible for the acts of our citizens, beyond our jurisdiction, is a question which opens a wide field for discussion, and is one which cannot be discussed in these cursory letters. All I shall say, is, that Mexico had the same right to complain that Spain had, and no more and even less, for it was the consequence of her own act, in calling in our countrymen to help her against Spain. I avoid saying any thing here, as to the merits of the quarrel between Texas and Mexico.