Other occurrences, however, had in the mean time taken place, which materially increased the difficulties attending the territorial question. The subject of slavery had for fifteen or twenty years been agitated with steadily increasing warmth, and for the latter portion of the period with growing violence. On the acquisition of the Mexican provinces, the representatives of the non-slaveholding States generally deemed it their duty to introduce into the acts passed for their government a restriction analogous to the antislavery proviso of the Ordinance of 1787. A motion to this effect having been made by Mr. Wilmot of Pennsylvania, by way of amendment to one of the appropriation bills passed during the war, the restriction has obtained the name of the "Wilmot Proviso." This motion in the House of Representatives was extensively seconded by the press, by popular assemblies, and by legislative resolutions throughout the non-slaveholding States, and caused a considerable increase of antislavery agitation. The South, of course, took an interest in the question not inferior to that of the North. The extension of the United States on the southwestern frontier has long been a cardinal point in the policy of most Southern statesmen. The application of an antislavery proviso to territories acquired by conquest in that quarter came into direct conflict with this policy. Meetings were accordingly held at Washington during the first session of the Thirtieth Congress, attended by a majority of the members from the slaveholding States, to take into consideration the measures proper to be adopted. At one of these meetings a sub-committee was appointed, of which Mr. Calhoun was chairman, to prepare an address "of the Southern delegates to their constituents." At a subsequent meeting a substitute for this address was submitted by Mr. Berrien of Georgia, under the title of an address "to the people of the United States." The original paper was, however, adopted in preference, and received the signatures of forty-eight of the members of Congress from the slaveholding States. Of these all but two were of the Democratic party.[30] These proceedings contributed materially to increase the discontents existing at the South. Nor was the progress of excitement less rapid at the North. The nomination of General Taylor by the Whig convention, accompanied by the refusal of that convention to countenance the Wilmot Proviso, led to the organization of the Free Soil party in the non-slaveholding States. In the summer of 1848, a convention of delegates of this party assembled at Buffalo in New York, at which an antislavery platform was adopted, and Mr. Van Buren was nominated as a candidate for the Presidency.