In September, 1845, the President of the United States directed their consul at Mexico to ascertain from the Mexican Government, whether it would receive an Envoy from the United States, intrusted with full power to adjust all the questions in dispute between the two Governments.

The answer of Mr. De la Pena y Pena, Minister of the Foreign Relations of Mexico, was, "That although the Mexican nation was deeply injured by the United States, through the acts committed by them in the department of Texas, which belongs to his nation, his Government was disposed to receive the Commissioner of the United States who might come to the capital, with full powers from his Government to settle the present dispute in a peaceful, reasonable and honorable manner;" thus giving a new proof that, even in the midst of its injuries and of its firm decision to exact adequate reparation for them, the Government of Mexico does not reply with contumely to the measures of reason and peace to which it was invited by its adversary.

The Mexican Minister at the same time intimated, that the previous recall of the whole Naval force of the United States, then lying in sight of the port of Vera Cruz, was indispensable; and this was accordingly done by our Government.

But it is essential to observe that, whilst Mr. Black had, according to his instructions, inquired, whether the Mexican Government would receive an Envoy from the United States, with full power to adjust all the questions in dispute between the two Governments, the Mexican Minister had answered, that his Government was disposed to receive the Commissioner of the United States, who might come with full powers to settle the present dispute in a peaceful, reasonable and honorable manner.

Mr. Slidell was, in November following, appointed Envoy Extraordinary and Minister Plenipotentiary of the United States of America near the Government of the Mexican Republic; and he arrived in Mexico on the sixth of December.

Mr. Herrera, the President of Mexico, was undoubtedly disposed to settle the disputes between the two countries. But taking advantage of the irritation of the mass of the people, his political opponents were attempting to overset him for having made, as they said, unworthy concessions. The arrival of Mr. Slidell disturbed him extremely; and Mr. Pena y Pena declared to Mr. Black, that his appearance in the capital at this time might prove destructive to the Government, and thus defeat the whole affair. Under these circumstances General Herrera complained, without any foundation, that Mr. Slidell had come sooner than had been understood; he resorted to several frivolous objections against the tenor of his powers; and he intimated that the difficulties respecting Texas must be adjusted before any other subject of discussion should be taken into consideration.But the main question was, whether Mexico should receive Mr. Slidell in the character of Envoy Extraordinary and Minister Plenipotentiary, to reside in the republic. It was insisted by the Mexican Government, that it had only agreed to receive a commissioner, to treat on the questions which had arisen from the events in Texas; and that until this was done, the suspended diplomatic intercourse could not be restored, and a residing minister plenipotentiary be admitted.

Why our Government should have insisted, that the intended negotiation should be carried on by a residing Envoy Extraordinary and Minister Plenipotentiary, is altogether unintelligible. The questions at issue might have been discussed and settled as easily, fully and satisfactorily, by commissioners appointed for that special purpose, as by residing ministers or envoys. It is well known that whenever diplomatic relations have been superseded by war, treaties of peace are always negotiated by commissioners appointed for that special purpose, who are personally amply protected by the law of nations, but who are never received as resident ministers, till after the peace has restored the ordinary diplomatic intercourse. Thus the treaty of peace of 1783, between France and England, was negotiated and concluded at Paris by British commissioners, whom it would have been deemed absurd to admit as resident envoys or ministers, before peace had been made.

The only distinction which can possibly be made between the two cases is, that there was not as yet actual war between Mexico and the United States. But the annexation of Texas was no ordinary occurrence. It was a most clear act of unprovoked aggression; a deep and most offensive injury; in fact, a declaration of war, if Mexico had accepted it as such. In lieu of this, that country had only resorted to a suspension of the ordinary diplomatic relations. It would seem as if our Government had considered this as an act of unparalleled audacity, which Mexico must be compelled to retract, before any negotiations for the arrangement of existing difficulties could take place; as an insult to the Government and to the nation, which must compel it to assert its just rights and to avenge its injured honor.

General Herrera was not mistaken in his anticipations. His government was overset in the latter end of the month of December, 1845, and fell into the hands of those who had denounced him for having listened to overtures of an arrangement of the difficulties between the two nations.

When Mexico felt its inability to contend with the United States; and, instead of considering the annexation of Texas to be, as it really was, tantamount to a declaration of war, only suspended the ordinary diplomatic relations between the two countries, its Government, if directed by wise counsels, and not impeded by popular irritation, should at once, since it had already agreed to recognize the independence of Texas, have entered into a negotiation with the United States. At that time there would have been no intrinsic difficulty in making a final arrangement founded on an unconditional recognition of the independence of Texas, within its legitimate boundaries. Popular feeling and the ambition of contending military leaders, prevented that peaceable termination of those unfortunate dissensions.

Yet, when Mexico refused to receive Mr. Slidell as an Envoy Extraordinary and Minister Plenipotentiary, the United States should have remembered, that we had been the aggressors, that we had committed an act acknowledged, as well by the practical law of nations, as by common sense and common justice, to be tantamount to a declaration of war; and they should have waited with patience, till the feelings excited by our own conduct had subsided.

General Taylor had been instructed by the War Department, as early as May 28, 1845, to cause the forces under his command to be put into a position where they might most promptly and efficiently act in defence of Texas, in the event that it should become necessary or proper to employ them for that purpose. By subsequent instructions, and after the people of Texas had accepted the proposition of annexation, he was directed to select and occupy a position adapted to repel invasion, as near the boundary line, the Rio Grande, as prudence would dictate; and that, with this view, a part of his forces at least should be west of the river Nueces. It was certainly the duty of the President to protect Texas against invasion, from the moment it had been annexed to the United States; and as that republic was in actual possession of Corpus Christi, which was the position selected by General Taylor, there was nothing, in the position he had taken, indicative of any danger of actual hostilities.

But our Government seems to have considered the refusal, on the part of Mexico, to receive Mr. Slidell as a resident Envoy of the United States, as necessarily leading to war. The Secretary of State, in his letter to Mr. Slidell of January 28, 1846, says:—"Should the Mexican Government finally refuse to receive you, the cup of forbearance will then have been exhausted. Nothing can remain but to take the redress of the injuries to our citizens, and the insults to our Government, into our own hands." And again, "Should the Mexican Government finally refuse to receive you, then demand passports from the proper authority, and return to the United States. It will then become the duty of the President to submit the whole case to Congress, and call upon the nation to assert its just rights, and avenge its injured honor."

With the same object in view, the Secretary of War did, by his letter dated January 13, 1846, instruct General Taylor "to advance and occupy, with the troops under his command, positions on or near the east bank of the Rio del Norte.... It is presumed Point Isabel will be considered by you an eligible position. This point, or some one near it, and points opposite Matamoras and Mier, and in the vicinity of Laredo, are suggested for your consideration.... Should you attempt to exercise the right, which the United States have in common with Mexico, to the free navigation of this river, it is probable that Mexico would interpose resistance. You will not attempt to enforce this right without further instructions.... It is not designed, in our present relations with Mexico, that you should treat her as an enemy; but, should she assume that character by a declaration of war, or any open act of hostility towards us, you will not act merely on the defensive if your relative means enable you to do otherwise."

The administration was therefore of opinion, that this military occupation of the territory in question was not an act of hostility, towards Mexico, or treating her as an enemy. Now, I do aver, without fear of contradiction, that whenever a territory claimed by two powers is, and has been for a length of time in the possession of one of them, if the other should invade and take possession of it by a military force, such an act is an open act of hostility according to the acknowledged and practical law of nations. In this case the law of nations only recognizes a clear and positive fact.

The sequel is well known. General Taylor, with his troops, left Corpus Christi, March 8th to 11th, 1846, and entered the desert which separates that place from the vicinity of the del Norte. On the 21st he was encamped three miles south of the Arroyo, or Little Colorado, having by the route he took marched 135 miles, and being nearly north of Matamoras about thirty miles distant. He had on the 19th met a party of irregular Mexican cavalry, who informed him that they had peremptory orders, if he passed the river, to fire upon his troops, and that it would be considered a declaration of war. The river was however crossed without a single shot having been fired. In a proclamation issued on the 12th, General Mejia, who commanded the forces of the Department of Tamaulipas, asserts, that the limits of Texas are certain and recognized, and never had extended beyond the river Nueces, that the cabinet of the United States coveted the regions on the left bank of the Rio Bravo, and that the American army was now advancing to take possession of a large part of Tamaulipas. On the 24th March General Taylor reached a point on the route from Matamoras to Point Isabel, eighteen miles from the former, and ten from the latter place, where a deputation sent him a formal Protest of the Prefect of the Northern District of the Department of Tamaulipas, declaring, in behalf of the citizens of the district, that they never will consent to separate themselves from the Mexican Republic, and to unite themselves with the United States. On the 12th of April, the Mexican General, Ampudia, required General Taylor to break up his camp within twenty-four hours, and to retire to the other bank of the Nueces river, and notified him that, if he insisted in remaining upon the soil of the Department of Tamaulipas, it would clearly result that arms alone must decide the question; in which case, he declared that the Mexicans would accept the war to which they had been provoked. On the 24th of April, General Arista arrived in Matamoras, and on the same day, informed General Taylor, that he considered hostilities commenced, and would prosecute them. On the same day, a party of sixty-three American dragoons, who had been sent some distance up the left bank of the river, became engaged with a very large force of the enemy, and after a short affair, in which about sixteen were killed or wounded, were surrounded and compelled to surrender. These facts were laid before Congress by the President in his message of the 11th of May.