Question

first text
i would save the union. i would save it the shortest way under the constitution. the sooner the national authority can be restored; the nearer the union will be \the union as it was.\ there be those who would not save the union, unless they could at the same time save slavery, i do not agree with them. if there be those who would not save the union unless they could at the same time destroy slavery, i do not agree with them. my paramount object in this struggle is to save the union, and is not either to save or to destroy slavery. if i could save the union without freeing any slave i would do it, and if i could save it by freeing all the slaves i would do it; and if i could save it by freeing some and leaving others alone i would also do that.
—from \letter to horace greeley, 1862\ by abraham lincoln
second text
the greatest social problem before the american people to - day is, as it has been for a hundred years, the presence among us of the negro. no comparable entanglement was ever drawn round itself by any other modern nation with so serene a disregard of its ultimate issue, or with a more distinct national responsibility. the african slave was brought here by cruel force, and with everybodys consent except his own. everywhere the practice was favored as a measure of common aggrandizement. when a few men and women protested, they were mobbed in the public interest with the public consent. there rests, therefore, a moral responsibility on the whole nation never to lose sight of the results of african - american slavery until they cease to work mischief and injustice.
—from \george washington cable, 1855\ by george washington cable
what topic do both men address?
the most significant problem facing the nation of the united state
the effects of slavery on the people of the united states

Explanation:

Lincoln focuses on saving the Union and his stance on slavery in relation to that goal. Cable emphasizes the social problem of the presence of African - Americans due to slavery and the nation's moral responsibility. Both are concerned with major issues facing the United States, with Lincoln on the Union and Cable on the social problem of race related to slavery.

Answer:

the most significant problem facing the nation of the United States