The provinces of New Mexico and the Californias are contiguous to the territories of the United States, and if brought under the government of our laws their resources - mineral, agricultural, manufacturing, and commercial - would soon be developed.

Upper California is bounded on the north by our Oregon possessions, and if held by the United States would soon be settled by a hardy, enterprising, and intelligent portion of our population. The bay of San Francisco and other harbors along the Californian coast would afford shelter for our Navy, for our numerous whale ships, and other merchant vessels employed in the Pacific Ocean, and would in a short period become the marts of an extensive and profitable commerce with China and other countries of the East.

These advantages, in which the whole commercial world would participate, would at once be secured to the United States by the cession of this territory; while it is certain that as long as it remains a part of the Mexican dominions they can be enjoyed neither by Mexico herself nor by any other nation.

In proposing to acquire New Mexico and the Californias, it was known that but an inconsiderable portion of the Mexican people would be transferred with them, the country embraced within these provinces being chiefly an uninhabited region.

These were the leading considerations which induced me to authorize the terms of peace which were proposed to Mexico. They were rejected, and negotiations being at an end, hostilities were renewed. An assault was made by our gallant Army upon the strongly fortified places near the gates of the city of Mexico and upon the city itself, and after several days of severe conflict the Mexican forces, vastly superior in number to our own, were driven from the city, and it was occupied by our troops.

Immediately after information was received of the unfavorable result of the negotiations, believing that his continued presence with the Army could be productive of no good, I determined to recall our commissioner. A dispatch to this effect was transmitted to him on the 6th of October last. The Mexican government will be informed of his recall, and that in the existing state of things I shall not deem it proper to make any further overtures of peace, but shall be at all times ready to receive and consider any proposals which may be made by Mexico.

A war of conquest is bad; but the present war has darker shadows. It is a war for the extension of slavery over a territory which has already been purged by Mexican authority from this stain and curse. Fresh markets of human beings are to be established; further opportunities for this hateful traffic are to be opened; the lash of the overseer is to be quickened in new regions; and the wretched slave is to be hurried to unaccustomed fields of toil. It can hardly be believed that now, more than eighteen hundred years since the dawn of the Christian era, a government, professing the law of charity and justice, should be employed in war to extend an institution which exists in defiance of these sacred principles.

It has already been shown that the annexation of Texas was consummated for this purpose. The Mexican War is a continuance, a prolongation, of the same efforts; and the success which crowned the first emboldens the partisans of the latter, who now, as before, profess to extend the area of freedom, while they are establishing a new sphere for slavery.

The authorities already adduced in regard to the objects of annexation illustrate the real objects of the Mexican War. Declarations have also been made, upon the floor of Congress, which throw light upon it. Mr. Sims, of South Carolina, has said that "he had no doubt that every foot of territory we shall permanently occupy, south of thirty-six degrees thirty minutes, will be slave territory"; and, in reply to his colleague, Mr. Burt, who inquired whether this opinion was "in consequence of the known determination of the Southern people that their institutions shall be carried into that country, if acquired," said, in words that furnish a key to the whole project, "It is founded on the known determination of the Southern people that their institutions shall be carried there; it is founded in the laws of God, written on the climate and soil of the country: nothing but slave labor can cultivate, profitably, that region of country."

But it is not merely proposed to open new markets for slavery: it is also designed to confirm and fortify the "Slave Power." Here is a distinction which should not fail to be borne in mind. Slavery is odious as an institution, if viewed in the light of morals and Christianity. On this account alone we should refrain from rendering it any voluntary support. But it has been made the basis of a political combination, to which has not inaptly been applied the designation of the "Slave Power."

The slaveholders of the country - who are not supposed to exceed 200,000 or at most 300,000 in numbers - by the spirit of union which animates them, by the strong sense of a common interest, and by the audacity of their leaders, have erected themselves into a new "estate," as it were, under the Constitution. Disregarding the sentiments of many of the great framers of that instrument, who notoriously considered slavery as temporary, they proclaim it a permanent institution; and, with a strange inconsistency, at once press its title to a paramount influence in the general government, while they deny the right of that government to interfere, in any way, with its existence. According to them, it may never be restrained or abolished by the general government, though it may be indefinitely extended.

If I devote myself to other pursuits and contemplations, I must first see, at least, that I do not pursue them sitting upon another man's shoulders. I must get off him first, that he may pursue his contemplations too. See what gross inconsistency is tolerated. I have heard some of my townsmen say, "I should like to have them order me out to help put down an insurrection of the slaves, or to march to Mexico -see if I would go"; and yet these very men have each, directly by their allegiance, and so indirectly, at least, by their money, furnished a substitute. The soldier is applauded who refuses to serve in an unjust war by those who do not refuse to sustain the unjust government which makes the war; is applauded by those whose own act and authority he disregards and sets at naught; as if the state were penitent to that degree that it hired one to scourge it while it sinned, but not to that degree that it left off sinning for a moment. Thus, under the name of Order and Civil Government, we are all made at last to pay homage to and support our own meanness. After the first blush of sin comes its indifference; and from immoral it becomes, as it were, unmoral, and not quite unnecessary to that life which we have made.