From what precedes it appears, that the Government of the United States considered the refusal of Mexico to receive a resident Envoy, or minister as a sufficient cause for war; and the Rio del Norte as the legitimate boundary of Texas. The first opinion is now of no importance; but the question of boundary, which was the immediate cause of hostilities, has to this day been the greatest impediment to the restoration of peace. I feel satisfied, that if this was settled, there would be no insuperable difficulty in arranging other pretensions.

The United States claim no other portion of the Mexican dominions, unless it be by right of conquest. The tract of country between the Rio Nueces and the del Norte, is the only one, which has been claimed by both parties, as respectively belonging either to Texas or to Mexico. As regards every other part of the Mexican possessions, the United States never had claimed any portion of it. The iniquity of acquiring any portion of it, otherwise than by fair compact freely consented to by Mexico, is self-evident. It is, in every respect, most important to examine the grounds on which the claim of the United States to the only territory claimed by both nations is founded. It is the main question at issue.

The Republic of Texas did, by an act of December 1836, declare the Rio del Norte to be its boundary. It will not be seriously contended, that a nation has a right, by a law of its own, to determine what is or shall be the boundary between it and another country. The act was nothing more than the expression of the wishes or pretensions of the Government. Its only practical effect was that, emanating from its Congress or legislative body, it made it imperative on the Executive, not to conclude any peace with Mexico, unless that boundary was agreed to. As regards right, the act of Texas is a perfect nullity. We want the arguments and documents by which the claim is sustained.

On a first view the pretension is truly startling. There is no exception: the Rio Norte from its source to its mouth is declared to be the rightful boundary of Texas. That river has its source within the department, province, or state of New Mexico, which it traverses through its whole length from north to south, dividing it into two unequal parts. The largest and most populous, including Santa Fe, the capital, lies on the left bank of the river, and is therefore embraced within the claim of Texas. Now this province of New Mexico was first visited and occupied by the Spaniards under Vasquez Coronado, in the years 1540 to 1542. It was at that time voluntarily evacuated, subsequently re-visited, and some settlements made about the year 1583: finally conquered in 1595 by the Spaniards, under the command of Onate. An insurrection of the Indians drove away the Spaniards in the year 1680. They re-entered it the ensuing year, and after a long resistance re-conquered it. This was an internal conflict with the Aborigines; but as related to foreign powers, the sovereignty of the Spaniards over the territory was never called in question; and it was, in express terms, made the western boundary of Louisiana in the Royal Charter of the French Government.

The conquest of the province by Onate, took place five-and-twenty years prior to the landing of the Pilgrims in New England, and twelve years before any permanent settlement had been made in North America, on the shores of the Atlantic, by either England, France, Holland, Sweden, or any other power, but that in Florida by Spain herself.

I have in vain sought for any document, emanating from the Republic or State of Texas, for the purpose of sustaining its claim either to New Mexico or to the country bordering on the lower portion of the del Norte. The only official papers within my reach, in which the claim of Texas is sustained, are the President's messages of May 11 and Dec. 3rd, 1846; and these refer only to the country bordering on the lower part of the del Norte. The portion of the message of May 11th, 1846, relating to that subject, is as follows: "Meantime Texas, by the final action of our Congress, had become an integral part of our Union. The Congress of Texas, by its act of December 19, 1836, had declared the Rio del Norte to be the boundary of that republic. Its jurisdiction had been extended and exercised beyond the Nueces. The country between that river and the del Norte had been represented in the Congress and in the Convention of Texas; had thus taken part in the act of annexation itself; and is now included within one of our congressional districts. Our own Congress had, moreover, with great unanimity, by the act approved December 31, 1845, recognized the country beyond the Nueces as a part of our territory, by including it within our own revenue system; and a revenue officer, to reside within that district, has been appointed, by and with the advice and consent of the Senate. It became, therefore, of urgent necessity to provide for the defence of that portion of our country. Accordingly, on the 13th of January last, instructions were issued to the general in command of these troops to occupy the left bank of the del Norte....

The movement of the troops to the del Norte was made by the commanding general, under positive instructions to abstain from all aggressive acts towards Mexico or Mexican citizens, and to regard the relations between that Republic and the United States as peaceful, unless she should declare war, or commit acts of hostility indicative of a state of war. He was specially directed to protect private property, and respect personal rights."

In his annual message of December 8, 1846, the President states that Texas, as ceded to the United States by France in 1803, has been always claimed as extending west to the Rio Grande; that this fact is established by declarations of our Government during Mr. Jefferson's and Mr. Monroe's administrations; and that the Texas which was ceded to Spain by the Florida treaty of 1819, embraced all the country now claimed by the State of Texas between the Nueces and the Rio Grande.

He then repeats the Acts of Texas with reference to their boundaries; stating that "during a period of more than nine years, which intervened between the adoption of her constitution and her annexation as one of the States of our Union, Texas asserted and exercised many acts of sovereignty and jurisdiction over the territory and inhabitants west of the Nueces; such as organizing and defining limits of counties extending to the Rio Grande; establishing courts of justice, and extending her judicial system over the territory; establishing also a custom-house, post-offices, a land-office, &c."

The President designates by the name of Texas, the cession of Louisiana by France to the United States; and he again calls the territory ceded to Spain by the Florida treaty of 1819, the Texas. He intimates that the claim of the United States to the territory between the Sabine and the Rio Norte, was derived from the boundaries of Texas, and that by claiming as far west as this river, the United States did recognize that it was the boundary of the Texas. I really do not understand what is meant by this assertion.

The United States claimed the Rio Norte as being the legitimate boundary of Louisiana, and not of Texas. Neither they nor France had ever been in possession of the country beyond the Sabine. Spain had always held possession, and had divided the territory into provinces as she pleased. One of these was called Texas, and its boundaries had been designated and altered at her will. With these the United States had no concern. If their claim could be sustained, it must be by proving that Louisiana extended of right thus far. This had no connection with the boundaries which Spain might have assigned to her province of Texas. These might have extended beyond the Rio del Norte, or have been east of the Rio Nueces. There is not the slightest connection between the legitimate boundaries of Louisiana, and those of the Spanish province of Texas. The presumed identity is a mere supposition.

It is not necessary to discuss the soundness of the pretensions to the Rio Norte, asserted by Mr. Jefferson and Mr. Monroe, since they were yielded in exchange of Florida and some other objects by the treaty of 1819; a treaty extremely popular at the time, and the execution of which was pressed with great zeal and perseverance.

Whenever ultimately ceded to Mexico, that republic fixed its boundaries as it thought proper. Texas and Cohahuila were declared to form a state; and the Rio Nueces was, made the boundary of Texas. When Texas declared itself independent, it was the insurrection of only part of a state; for Cohahuila remained united to Mexico. But the Rio Nueces was the boundary between the department of Texas and the state of Tamaulipas. The whole contested territory lies within the limits of Tamaulipas, which never was, under the Mexican Government, connected in any shape with Texas.

The question now under consideration is only that between the United States and Mexico; and in that view of the subject, it is quite immaterial whether the acts of the United States emanated from Congress, or from the Executive. No act of either, recognizing the country beyond the Nueces, as a part of the territory of the United States, can be alleged against Mexico, as a proof of their right to the country thus claimed. Any such act is only an assertion, a declaration, but not an argument sustaining the right. It is, however, proper to observe here, that the port of delivery west of the Nueces, erected by the act of Congress "To establish a collection district in the state of Texas," was at Corpus Christi, a place which was in the actual possession of that state.

It must also be premised that, in the joint resolution for the annexation of Texas, the question of the boundary between it and Mexico was expressly reserved, as one which should be settled by treaty between the United States and Mexico.

The only arguments in the President's message, which sustain the right of Texas to territory beyond the Nueces, are contained in those passages, in which it is asserted, that the jurisdiction of Texas had been extended and exercised beyond the Nueces: that the country between that river and the del Norte had been represented in the Congress and Convention of Texas, had taken part in the annexation itself, and was now included within one of our congressional districts.

But it is not stated in the President's message, how far beyond the Nueces, the jurisdiction of Texas had been extended, nor what part of the country between that river and the del Norte had been represented in the Congress and convention of Texas, and was then included within one of our congressional districts.

Now the actual jurisdiction beyond the Nueces never extended farther than the adjacent settlement of San Patricio, consisting of about twenty families. That small district, though beyond the Nueces, was contiguous to, and in the actual possession of Texas. On this account it might be rightfully included within the limits, which we were bound to protect against Mexican invasion.

But what was the country between this small settlement of San Patricio, or between Corpus Christi and the Rio del Norte, over which it might be supposed from the message, that the jurisdiction of Texas had been extended; so as to be included within one of our congressional districts? Here again, Texas had erected that small settlement into a county called San Patricio, and declared that this county extended to the Rio del Norte. This, like all other declaratory acts of the same kind, was only an assertion not affecting the question of right. The State of Texas might, with equal propriety, have declared that their boundary extended to the Sierra Madre or to the Pacific. The true question of right to any territory beyond the Mexican limits of the Department of Texas depends on the facts: By whom was the territory in question actually inhabited and occupied? and had the inhabitants united with Texas in the insurrection against Mexico?

The whole country beyond the settlement of San Patricio and Corpus Christi, till within a few miles of the del Norte, is a perfect desert, one hundred and sixty miles wide by the route pursued by General Taylor, as stated by himself, and near one hundred and twenty miles in a straight line.

The only settled part of it is along the left bank of the del Norte, and but a few miles in breadth. This belt was settled, inhabited, and occupied exclusively by Mexicans. It included the town of Loredo; and Mexico had a custom-house at Brazos, north of the mouth of the river. Till occupied by the American arms it had ever been, and was at the time when invaded by General Taylor, a part of the Department of Tamaulipas, and subject to the jurisdiction of the Prefect of the Northern District of that department.

In the course of the war between Mexico and Texas, incursions had been occasionally made by each party into the territories of the other. A Mexican officer had, once or twice, obtained temporary occupation of San Antonio, within the limits of Texas; and the Texans had on one occasion taken Loredo itself, and more than once had carried their arms, not only to the left bank of the del Norte, but even beyond that river. In both cases the aggressive parties had been repulsed and expelled. The last Texan expedition of that kind took place in December, 1842, and terminated in their defeat at Mier.

That the country, adjacent to the left bank of the river, was exclusively in the possession of the Mexicans, was well known to our Government.

When General Taylor marched to the del Norte, he issued an order (No. 30), translated into the Spanish, ordering all under his command, to observe with the most scrupulous respect the rights of all the inhabitants, who might be found in peaceful prosecution of their respective occupations, as well on the left as on the right side of the Rio Grande. No interference, he adds, will be allowed with the civil rights or religious privileges of the inhabitants.

In June, 1845, General Taylor had been directed to select and occupy, on or near the Rio Grande del Norte, such a site as would be best adapted to repel invasion and to protect our Western bor der. But on the 8th of July following, the Secretary of War (Mr. Marcy) addressed the following letter to him.

"This Department is informed that Mexico has some military establishments on the East side of the Rio Grande, which are, and for some time have been, in the actual occupancy of her troops. In carrying out the instructions heretofore received, you will be careful to avoid any acts of aggression, unless an actual state of war should exist. The Mexican forces at the posts in their possession, and which have been so, will not be disturbed as long as the relations of peace between the United States and Mexico continue."

On the 30th July, 1845, the Secretary again addresses Gen. Taylor as follows: "You are expected to occupy, protect and defend the territory of Texas, to the extent that it has been occupied by the people of Texas. The Rio Grande is claimed to be the boundary between the two countries, and up to this boundary you are to extend your protection, only excepting any posts on the Eastern side thereof, which are in the actual occupancy of Mexican forces, or Mexican settlements, over which the Republic of Texas did not exercise jurisdiction at the period of annexation, or shortly before that event. It is expected, in selecting the establishment for your troops, you will approach as near the boundary line, the Rio Grande, as prudence will dictate. With this view, the President desires that your position, for a part of your forces at least, should be west of the River Nueces."

The Mexican settlements, thus excepted, are not those over which Texas did not claim jurisdiction, but those on the East bank of the Rio Grande, over which Texas did not exercise jurisdiction at the period mentioned. The President had no authority to give up the boundary claimed by Texas; but it is clear that at the time, when war was not contemplated, the Administration was of opinion that, till the question was definitively settled, the occupancy by the Mexicans of the territory adjacent the left bank of the del Norte ought not to be disturbed. Neither the subsequent refusal by Mexico to receive a residing Envoy, nor the successes of the American arms have affected the question of right. The claim of Texas, whether to New Mexico, or to the lower portion of the Rio Norte, was identically the same, as invalid and groundless in one case as in the other. Why a distinction has been made by the Executive has not been stated. The fact is that he has established a tempo rary government for New Mexico, as a country conquered, and without any regard to the claim of Texas; whilst, on the other hand, he has permitted that State to extend its jurisdiction over the country lying on the left bank of the del Norte, which, like New Mexico, had been conquered by the arms of the United States. Not a shadow of proof has been adduced to sustain the pretensions of Texas to that district; and justice imperiously requires that it should by the treaty of peace be restored to Mexico.

It so happens that the boundary, which may be traced in conformity with this principle, is a natural one, and that, as a measure of expediency, none more eligible could have been devised. A desert of one hundred and twenty miles separates the most Southwesterly Texan settlements of Corpus Christi and San Patricio, from those of the Mexicans, on the left bank of the del Norte, than which no boundary could be devised, better calculated to prevent collisions hereafter between the two nations. It will be sufficient, for that purpose, to draw a nominal line through the desert, leaving all the waters that empty into the Rio Norte to Mexico, and all those that empty into the Rio Nueces to Texas, together with such other provisions, respecting fortifications and military posts, as may be necessary for the preservation of peace.

The line of the Rio Norte is one, from which Mexico would be perpetually threatened, and from which their adjacent town on the eastern bank may be bombarded. Such an intolerable nuisance would perpetuate most hostile feelings. With such a narrow river as the Rio del Norte, and with a joint right of navigation, repeated collisions would be unavoidable.

Among these, when there was nothing but a fordable river to cross, slaves would perpetually escape from Texas: and where would be the remedy? Are the United States prepared to impose by a treaty on Mexico, where slavery is unknown, the obligation to surrender fugitive slaves?

Mexico is greatly the weaker power, and requires a boundary, which will give her as much security as is practicable. It is not required, either for the preservation of peace, or for any other legitimate purpose, that the United States should occupy a threatening position. It cannot be rationally supposed, that Mexico will ever make an aggressive war against them; and even in such case, the desert would protect them against an invasion. If a war should ever again take place between the two countries, the over whelming superiority of the Navy of the United States will enable them to carry on their operations wherever they please. They would, within a month, re-occupy the left bank of the Rio Norte, and within a short time, effect a landing and carry the war to any quarter they pleased.

Must the war be still prosecuted for an object of no intrinsic value, to which the United States have no legitimate right, which justice requires them to yield, and which even expediency does not require?