But the hold of this policy on the South was soon afterwards undermined by the economic development which followed the introduction of the cotton-gin. The new and rapidly growing prosperity of the planter depended on the permanence of the "institution". And from this time forward the Southern policy becomes hard to distinguish from the vested interests of the slave-owner. The prosperity of the South seemed to depend upon the extension of the cotton industry: the cotton industry, again, upon slave-labour; thus it was argued, the institution of slavery was necessary to the prosperity of the South. The North, so the Southerner supposed, had its own interests to serve, and only regarded the South as a market. It was, he felt, jealous of the dominance of Southern statesmanship in the Union; and its desire to destroy "the institution" was denounced as the sectional jealousy of small-minded, shop-keeping bigots, of inferior antecedents. By the brute force of increasing numbers, by a vulgar love of trade, and the accidents of climate and of mineral resources, the North was beginning to establish its hold upon Congress, and arrogating to itself the Federal power. Hitherto, with the exception of the Adamses and of Jackson, every President had been of Virginian birth, bred, the Southerner declared, in the broader views of statesmanship. But the North was now predominant in the House of Representatives, and a balance could only be preserved in the Senate, where each State appoints two members, by constant watchfulness. Thus the rapid settling of the middle West by Northerners must be balanced by the annexation of new cotton-growing regions in the South-west. The famous Missouri Compromise of 1821 fixed the frontier between future free-soil and slave States at the line of the southern boundary of Missouri, while admitting that State itself into the Union as a member of the latter class. Hence it was only in the South-west that slavery could develop, and extension by conquest of cotton territory became henceforward an object of Southern politicians. While, then, it was the aggression of the South which finally drove the nation into civil war, the South for many years had viewed itself as an aggrieved partner in the inter-State compact, victimised in the interests of the majority. It felt, perhaps not unjustly, that it was being overridden, and that the Federation was becoming what Jefferson described as "a foreign yoke".[54] It became excessively sensitive to hostility: every rumour of the spread of Abolition sentiment in the North--a sentiment which favoured a new attitude towards the Federal power, and would give control to it over the domestic affairs of what hitherto had literally been "Sovereign States"--raised a storm of indignation and evoked new threats of secession. * * * * *