Question refers to the excerpt below. "That was a war of National defence, required for the vindication of the National rights and honor, and demanded by the indignant voice of the People. President [James] Madison … at first, reluctantly and with great doubt and hesitation, brought himself to the conviction that it ought to be declared. … It was a just war, and its great object, as announced at the time, was 'Free Trade and Sailors Rights,' against the intolerable and oppressive acts of British power on the ocean. The justice of the war, far from being denied or controverted, was admitted by the Federal party, which only questioned it on considerations of policy. … How totally variant is the present war! This is no war of defence, but one of unnecessary and of offensive aggression. It is Mexico that is defending her fi re-sides, her castles and her altars, not we. And how different also is the conduct of the Whig party of the present day from that of the major part o

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"That was a war of National defence, required for the vindication of the National rights and honor, and demanded by the indignant voice of the People. President [James] Madison ... at first, reluctantly and with great doubt and hesitation, brought himself to the conviction that it ought to be declared. ... It was a just war, and its great object, as announced at the time, was 'Free Trade and Sailors Rights,' against the intolerable and oppressive acts of British power on the ocean. The justice of the war, far from being denied or controverted, was admitted by the Federal party, which only questioned it on considerations of policy. ... How totally variant is the present war! This is no war of defence, but one of unnecessary and of offensive aggression. It is Mexico that is defending her fi re-sides, her castles and her altars, not we. And how different also is the conduct of the Whig party of the present day from that of the major part of the Federal party during the war of 1812! Far from interposing any obstacles to the prosecution of the war, if the Whigs in office are reproachable at all, it is for having lent too ready a facility to it, without careful examination into the objects of the war."—Henry Clay, Speech about the Mexican War, 1847

Clay's speech foreshadows the congressional debate over the...?

The  slavery in the Mexican Cession

Explanation:

Mexico's surrender during the Mexican War was accomplished with the signing of the Guadalupe-Hidalgo Treaty. In that treaty, Mexico assigned 525,000 square miles of territory to the United States in return for a payment of $ 15 million. This territory ceded to the USA, had a question about slavery that was not corresponding with the legislation of slavery in the USA.

This excerpt from Clay's speech foreshadows how the issue of slavery would be a problem to be solved in the USA later, in relation to the land donated by Mexico.

a goverment for the people by the people