This letter was addressed to Mr. Benjamin Green, the son of Mr. Duff Green; so that the beginning and the ending of this "immediate" annexation scheme, so far as the invention of the pretext, and the inculpation of Great Britain is concerned, is in the hands of father and son—a couple, of whom it may be said, in the language of Gil Blas, "These two make a pair." The letter itself is one of the most unfortunate that the annals of diplomacy ever exhibited. It admits the wrong to Mexico, and offers to fight her for that wrong; and not for any thing that she has done to the United States, but because of some supposed operation of Great Britain upon Texas. Was there ever such a comedy of errors, or, it may be, tragedy of crimes! Let us analyze this important letter; let us examine it, paragraph by paragraph.

The first paragraph enjoins the strongest assurances to be given to Mexico of our indisposition to wound the dignity or honor of Mexico in making this treaty, and of our regret if she should consider it otherwise. This admits that we have done something to outrage Mexico, and that we owe her a volunteer apology, to soften her anticipated resentment.

The same paragraph states that we have been driven to this step in self-defence, and to counteract the "policy adopted," and the "efforts made" by Great Britain to abolish slavery in Texas. This is an admission that we have done what may be offensive and injurious to Mexico, not on account of any thing she has done to us, but for what we fear Great Britain may do to Texas. And as for this plea of self-defence, it is an invasion of the homicidal criminal's prerogative, to plead it. All the murders committed in our country, are done in self-defence—a few through insanity. The choice of the defence lies between them, and it is often a nice guess for counsel to say which to take. And so it might have been in this case; and insanity would have been an advantage in the plea, being more honorable, and not more false.

The same paragraph admits that the United States has made this treaty in full view of war with Mexico; for the words "all possible consequences," taken in connection with the remaining words of the sentence, and with General Almonte's notice filed by order of his government at the commencement of this negotiation, can mean nothing else but war! and that to be made by the treaty-making power.

The second paragraph directs the despatch of Lord Aberdeen to be read to the Mexican Secretary of State, to show him our cause of complaint against Great Britain. This despatch is to be read—not delivered, not even a copy of it—to the Mexican minister. He may take notes of it during the reading, but not receive a copy, because it is a document to be sent to the Senate! Surely the Senate would have pardoned a departure from etiquette in a case where war was impending, and where the object was to convince the nation we were going to fight! that we had a right to fight her for fear of something which a third power might do to a fourth. To crown this scene, the reading is to be of a document in the English language, to a minister whose language is Spanish; and who may not know what is read, except through an interpreter.

The third paragraph of this pregnant letter admits that questions are to grow out of this treaty, for the settlement of which a minister will be sent by us to Mexico. This is a most grave admission. It is a confession that we commit such wrong upon Mexico by this treaty, that it will take another treaty to redress it; and that, as the wrong doer, we will volunteer an embassy to atone for our misconduct. Boundary is named as one of these things to be settled, and with reason; for we violate 2,000 miles of Mexican boundary which is to become ours by the ratification of this treaty, and to remain ours till restored to its proper owner by another treaty. Is this right? Is it sound in morals? Is it safe in policy? Would we take 2,000 miles of the Canadas in the same way? I presume not. And why not? why not treat Great Britain and Mexico alike? why not march up to "Fifty-Four Forty" as courageously as we march upon the Rio Grande? Because Great Britain is powerful, and Mexico weak—a reason which may fail in policy as much as in morals. Yes, sir! Boundary will have to be adjusted, and that of the Rio Grande; and until adjusted, we shall be aggressors, by our own admission, on the undisputed Mexican territory on the Rio Grande.

The last paragraph is the most significant of the whole. It is a confession, by the clearest inferences, that our whole conduct to Mexico has been tortuous and wrongful, and that she has "rights," to the settlement of which Mexico must be a party. The great admissions are, the want of the concurrence of Mexico; the want of her previous consent to this treaty; its objectionableness to her; the violation of her boundary; the "rights" of each, and of course the right of Mexico to settle questions of security and interest which are unsettled by the present treaty. The result of the whole is, that the war, in full view of which the treaty was made, was an unjust war upon Mexico.

Thus admitting our wrong in injuring Mexico, in not obtaining her concurrence; in not securing her previous consent; in violating her boundary; in proceeding without her in a case where her rights, security, and interests are concerned; admitting all this, what is the reason given to Mexico for treating her with the contempt of a total neglect in all this affair? And here strange scenes rise up before us. This negotiation began, upon the record, in August last. We had a minister in Mexico with whom we could communicate every twenty days. Mexico had a minister here, with whom we could communicate every hour in the day. Then why not consult Mexico before the treaty? Why not speak to her during these eight months, when in such hot haste to consult her afterwards, and so anxious to stop our action on the treaty till she was heard from, and so ready to volunteer millions to propitiate her wrath, or to conciliate her consent? Why this haste after the treaty, when there was so much time before? It was because the plan required the "bomb" to be kept back till forty days before the Baltimore convention, and then a storm to be excited.

The reason given for this great haste after so long delay, is that the safety of the United States was at stake: that the British would abolish slavery in Texas, and then in the United States, and so destroy the Union. Giving to this imputed design, for the sake of the argument, all the credit due to an uncontradicted scheme, and still it is a preposterous excuse for not obtaining the previous consent of Mexico. It turns upon the idea that this abolition of slavery in Texas is to be sudden, irresistible, irretrievable! and that not a minute was to be lost in averting the impending ruin! But this is not the case. Admitting what is charged—that Great Britain has adopted a policy, and made efforts to abolish slavery in Texas, with a view to its abolition in the United States—yet this is not to be done by force, or magic. The Duke of Wellington is not to land at the head of some 100,000 men to set the slaves free. No gunpowder plot, like that intended by Guy Fawkes, is to blow the slaves out of the country. No magic wand is to be waved over the land, and to convert it into the home of the free. No slips of magic carpet in the Arabian Nights is to be slipped under the feet of the negroes to send them all whizzing, by a wish, ten thousand miles through the air. None of these sudden, irresistible, irretrievable modes of operating is to be followed by Great Britain. She wishes to see slavery abolished in Texas, as elsewhere; but this wish, like all other human wishes, is wholly inoperative without works to back it: and these Great Britain denies. She denies that she will operate by works, only by words where acceptable. But admit it. Admit that she has now done what she never did before—denied her design! admit all this, and you still have to confess that she is a human power and has to work by human means, and in this case to operate upon the minds of people and of nations—upon Mexico, Texas, the United States, and slaves within the boundaries of these two latter countries. She has to work by moral means; that is to say, by operating on the mind and will. All this is a work of time—a work of years—the work of a generation! Slavery is in the constitution of Texas, and in the hearts, customs, and interests of the people; and cannot be got out in many years, if at all. And are we to be told that there was no time to consult Mexico? or, in the vague language of the letter, that circumstances did not permit the consultation, and that without disclosing what these circumstances were? It was last August that the negotiation began. Was there fear that Mexico would liberate Texian slaves if she found out the treaty before it was made? Alas! sir, she refused to have any thing to do with the scheme! Great Britain proposed to her to make emancipation of slaves the condition of acknowledging Texian independence. She utterly refused it; and of this our government was officially informed by the Earl of Aberdeen. No, sir, no! There is no reason in the excuse. I profess to be a man that can understand reason, and could comprehend the force of the circumstances which would show that the danger of delay was so imminent that nothing but immediate annexation could save the United States from destruction. But none such are named, or can be named; and the true reason is, that the Baltimore convention was to sit on the 27th of May.

Great Britain avows all she intends, and that is—a wish—TO SEE—slavery abolished in Texas; and she declares all the means which she means to use, and that is, advice where it is acceptable.