Mr. Editor: - In your paper of July f lili, it ismentioned, to the credit of the n Liberty party papers, that "only two of fj hem are supporters of the present vilainous war with Mexico." I was c irised to learn that there was even one f )f them, that would in the least palliate he exceeding injustice of our democratie President's furay upon that sister republic. For upon the Liberty party, must devolve the work of showing up the bold pro-slavery aspect of this nggressive movement upon n weak and wronged people. I propose to give your readers some facts, to show the object of President Polk's war upon Mexico. Tho papers are every day incidentally bringing to light, facts which when put togelher mako a slrong case. An article recently nppeared in the American Review prepared by the Hon. D. D. Barnard which insÃ¼tutes aseaiching scrutiny into the causes which led to the war. To that article I am indebted for several of ihe facts quoted in this communication. An impartial history of the difficulties between the United States and Mexico, will make it very evident that the latier has not desired to resort to arms for their settlement, and that she had done nothing to rende r war inevitable. She now regards herself as acting on the defensive - as repclling an invasiÃ³n upon her own soil. In the year 1839 a Convention was held at Washington, to determine tho amount of claims held by citizens of the United States against Mexico. A desire to allov what was fair and reasonable was manifestad by the Commissioners from that country. Not long alter, Mr. Waddy Thompson was appointed Minister near the government of that republic, one of the chief items of the business to which he had to attend being the settleinent of these claims. His mission terminated in March, 1844, just one month before Mr. Tyler's treaty for the Arinexation of Texas, was concluded. When aboul to leave Mexico, Mr. T. made an address, in which he said, "I have not made a single official demand, or even n. simple request which was not granted."In the same address he said - '-the bonds of friendship between ihe two nations had a been strengthened, insteadof bdng ii ened." Shortly after bis return to ihÃa i country, Mr. Thompson published a book, t in which he represents the Mexicans as r being amicably disposed towards this c country. In regard to the rumor of I thcir intention to attack Texas, he says, c "Nfot or.e man of sense in Mexico either i desires or antÃ¯cipates such a thing as the ( iavasion of Texas." "They are not t ing" said he "to declare war against us, ( I have never doubted for a moment about that." ( If this was the state of feeling among 1 the Mexicans, how does it happen that ] before many months had elapsed ourcan. i non are booming away at the walls of the fortified cities of Mexico? Why simply becauso all has been done that could be done to heap insult upon Mexico, and deceive the people of this country with the idea that Mexico has been the aggressor. Let us sce how very indicative of peaceful intentions have been the movements of our government. As soon as Texas was annexed it became necessary in the opiniÃ³n of President Polk, "Ã¡s a precautionary mensure, lo order a strong squadron to the coast of Mexico, and to concÃ©ntrate an efficiÃ«nt force on the western frontier of Texas." The very ftrst post to which he directed the army was within what had been regarded as Mexican territory. It was at any rate in territory which the most zeaious Annexalionists admitled to bestill in dispute. In a despatch to Gen. Taylor. the Secrotary of War says, "The President desires that your position ior a part of your forces at least, should be west of the river Neuces." The Neuces, it is to be observed, was regardod by the Texans themselves, as their Western boundary. It is about one hundred and fifty miles fÃ¯om Ã¼xo Rjo Grande. The Presidentcould not be ignorant that he ordercd ihe army inlo the country that the Mexi'-ans regarded as theirs, and tliat they could not look upon sucli a movemcnt without jealousy. And hadihey desired occasion for war they might have considered this as suiliciently provocative. In August last, Gen. Taylor staiioned his army at Corpus Christi, beyond the Neuces. Yet as long as he remained there, he saw no disposition to resist hun. On the Ãlh September following, Geu. T. writes thus: "I have the honor to report, that a confidential ogent dispatched some days si nee to IWulamoras has returned and roports that the garrison does not seem to have been increased, and that our consul is of opiniÃ³n there will be no declaration of war." He adds - "I must express the hope that no militia forcÃ© will be ordered lo join me withoutny requisition for t. I am entirely conÃ¯dent that none will be required." But this state of things was not all ac:ording to the mind of our Democratie President. The state of things was alogether too peaceful for his fancy. He hought of another plan by which he â night bring matters to a more warlike crisis. 11e sent a minister to the government of Mexico with the hope that he might be rejected, and in thia pretext for resorting to arms might be found. In his message to Congress, assigning reasons for this mission, he says: "After our army and navy, had remained on the frontier and coasts of Mexico for many weeks, without any hostile movemcnl 071 her part, I deemed it important to put an end to this state of things." Yes, this state of things in which there was no hostile movement must come lo an end. Henee the mission of the Hon. Mr. Slidell. lts unsatisfactory termination was doubtless not unsatisfactory to the Presdent. It resulted, as he had good reaosn to believe it would. With the return cf Mr. Slidell, a new movement was made against Mexico. Gen. Taylor was at once ordered "to npproach as near the Rio Grande as prudence will dÃctate," and was furlher told " you need not wait for directions from Washington to carry out what yon may deemproper to be done." Accordingly, about the first of March our army took up the Ã¼ne of march for tho Rio Grande, aad in a few weeks Gen. Taylor had placed himself in hostile array before Metamoras, the citizens of : Point Isabel hearing of his progress hav; ing in the meantime set fire to their dwellings and fled, fearing an attack from him. The Mexicans now thought that endurance was no longer a virtue, and prepared to defend themselves. But it .vill be seen in the next paper, that they did not commenco hostilities, but in a digni. C.A mnnor trOVfi tO aVCl't iheiÃ¯l.