Mr. Calhoun urged the scheme of annexation with intense earnestness. Taking up the subject where Mr. Upshur had left it, he conducted the negotiation with zeal and skill. His diplomatic correspondence was able and exhaustive. It was practically a frank avowal that Texas must be incorporated in the Union. He feared that European influence might become dominant in the new republic, and, as a consequence, that anti-slavery ideas might take root, and thence injuriously affect the interests, and to some extent the safety, of the Southern States. In an instruction to William R. King, our minister at Paris, Mr. Calhoun called his attention to the fact that England regarded the defeat of annexation "as indispensable to the abolition of slavery in Texas." He believed that England was "too sagacious not to see what a fatal blow abolition in Texas would give to slavery in the United States." Then, contemplating the effect of the general abolition of slavery, he declared that "to this continent it would be calamitous beyond description." It would "destroy in a great measure the cultivation and production of the great tropical staples, amounting annually in value to nearly $300,000,000." It is a suggestive commentary on Mr. Calhoun's evil foreboding, that the great tropical staple of the South has steadily increased in growth under free labor, and that the development of Texas never fairly began until slavery was banished from her soil. Discussing the right of Texas to independence, in an instruction to Wilson Shannon, our minister to Mexico, Mr. Calhoun averred that "Texas had never stood in relation to Mexico as a rebellious province struggling to obtain independence. The true relation between them is that of independent members of a federal government, the weaker of which has successfully resisted the attempts of the stronger to conquer and subject her to its power." This was applying to the constitution of Mexico the same construction which he had so long and so ably demanded for our own. It was, indeed, but a paraphrase of the State-sovereignty and State-rights theory, with which he had persistently indoctrinated the Southern mind. Ten years after Mr. Calhoun was in his grave, the same doctrine, in almost the same form of expression, became familiar to the country as the Southern justification for resorting to civil war.