“the result of that war {mexican war} was lamentable not only for our country but also lamentable for the reputation of the americans. the despoliation which we suffered was qualified as a real robbery even by citizens of that [wars] cost, also, much bloodshed which, when poured out in order to serve injustice and oppression, does not pay at all, for it does not even receive the applause of history." –mexican history textbook

identify a likely point of bias in the source material quoted above.

..."order to serve injustice and oppression, does not pay at all, for it does not even receive the applause of history."

This point qualifies as a biased source material. The Mexican History author distillate his own perspective about the outcome of the war. Judging by his declaration of Mexican heritage, (... not only for our country...) the author gives a very uncomfortable, and furious opinion about the American action during this war, and in the end makes a huge generalization about the viewpoint of other authors about this war. Mexican War resulted from the Annexation of Texas, declared by a joint resolution of Congress  in 1845, infuriated Mexico. The newly elected president, James K. Polk, sought  to acquire California and New Mexico as well as Texas, but negotiations soon  failed. When Mexican troops crossed the Rio Grande, Polk urged Congress to  declare war.

other sources of text

explanation:

this can be magazines, news reports, scholarly articles, textbooks, research papers etc.

ayatollah khomeini can best be described as the leader who declared iran to be an islamic republic.