Before long the frontier created a demand for merchants. As it retreated from the coast it became less and less possible for England to bring her supplies directly to the consumer's wharfs, and carry away staple crops, and staple crops began to give way to diversified agriculture for a time. The effect of this phase of the frontier action upon the northern section is perceived when we realize how the advance of the frontier aroused seaboard cities like Boston, New York, and Baltimore, to engage in rivalry for what Washington called "the extensive and valuable trade of a rising empire." The legislation which most developed the powers of the national government, and played the largest part in its activity, was conditioned on the frontier. Writers have discussed the subjects of tariff, land, and internal improvement, as subsidiary to the slavery question. But when American history comes to be rightly viewed it will be seen that the slavery question is an incident. In the period from the end of the first half of the present century to the close of the Civil War slavery rose to primary, but far from exclusive, importance. But this does not justify Dr. von Holst (to take an example) in treating our constitutional history in its formative period down to 1828 in a single volume, giving six volumes chiefly to the history of slavery from 1828 to 1861, under the title "Constitutional History of the United States." The growth of nationalism and the evolution of American political institutions were dependent on the advance of the frontier. Even so recent a writer as Rhodes, in his "History of the United States since the Compromise of 1850," has treated the legislation called out by the western advance as incidental to the slavery struggle. This is a wrong perspective. The pioneer needed the goods of the coast, and so the grand series of internal improvement and railroad legislation began, with potent nationalizing effects. Over internal improvements occurred great debates, in which grave constitutional questions were discussed. Sectional groupings appear in the votes, profoundly significant for the historian. Loose construction increased as the nation marched westward.[25:1] But the West was not content with bringing the farm to the factory. Under the lead of Clay--"Harry of the West"--protective tariffs were passed, with the cry of bringing the factory to the farm. The disposition of the public lands was a third important subject of national legislation influenced by the frontier.