For This Question,refer to the Following Two Excerpts

For this question,refer to the following two excerpts. Texas is now ours....The independence of Texas was complete and absolute.It was an independence,not only in fact,but of right....What then can be more preposterous than all this clamor by Mexico and the Mexican interest,against Annexation,as a violation of any rights of hers...?
Nor is there any just foundation for the charge that Annexation is a great pro-slavery measure-calculated to increase and perpetuate that institution.Slavery had nothing to do with it....That it will tend to facilitate and hasten the disappearance of Slavery from all the northern tier of the present Slave States,cannot surely admit of serious question.The greater value in Texas of the slave labor now employed in those States,must soon produce the effect of draining off that labor southwardly....
California will,probably,next fall away....Already the advance guard of the irresistible army of Anglo-Saxon emigration has begun to pour down upon it,armed with the plough and the rifle,and marking its trail with schools and colleges,courts and representative halls,mills and meeting-houses.A population will soon be in actual occupation of California....And they will have a right to independence-to self-government ...a better and a truer right than the artificial title of sovereignty in Mexico,a thousand miles distant,inheriting from Spain a title good only against those who have none better.
John L.O'Sullivan,Editor,"Manifest Destiny," from United States Magazine and Democratic Review,July 1845
If we regard Texas as a province of Mexico,its boundaries must be sought in the geography of that republic.If we regard it as an independent State,they must be determined by the extent of jurisdiction which the State was able to maintain.Now it seems clear that the river Nueces was always recognized by Mexico as the western boundary;and it is undisputed that the State of Texas,since its Declaration of Independence,never exercised any jurisdiction beyond the Nueces....
In the month of January,1846,the President of the United States directed the troops under General Taylor,called the Army of Occupation,to take possession of this region [west of the Nueces River].Here was an act of aggression.As might have been expected,it produced collision.The Mexicans,aroused in self-defence,sought to repel the invaders....
Here the question occurs,What was the duty of Congress in this emergency? Clearly to withhold all sanction to unjust war,-to aggression upon a neighboring Republic....The American forces should have been directed to retreat,not from any human force,but from wrongdoing;and this would have been a true victory.
Alas! This was not the mood of Congress.With wicked speed a bill was introduced,furnishing large and unusual supplies of men and money....This was adopted by a vote of 123 to 67;and the bill then leaped forth,fully armed,as a measure of open and active hostility against Mexico.
Charles Sumner,Conscience Whig and future Republican Senator from Massachusetts,Letter to Robert Winthrop,a Whig Congressman from Massachusetts,October 25,1846
The two excerpts quoted above would be most useful to historians analyzing

A) the attempts of the U.S.federal government to assert authority over the states.
B) U.S.government interaction and conflict with Hispanics.
C) the heated controversy generated by the acquisition of new territory in the West.
D) the variety of proposals made to resolve the issue of slavery in the territories.