President Jackson also had the nerve to veto the bill creating a national bank; and when, after two terms of service, he retired, he gave up to the rule of his designated successor a nation of fifteen millions of people, solvent, prosperous, and apparently destined to a long career of peace and power. The four years of President Van Buren's term were not notable for great events, and are chiefly interesting as exhibiting the re-formation of parties, in which the lines between the Whigs and the Democrats became more defined and distinct. Van Buren was the leader of the Democrats, but was soon to lose that leadership by reason of his connection with the fast-growing anti-slavery cause. Henry Clay was the Whig chief; and continued to be so, despite the rivalry of Webster, down to the time of his death. [Sidenote: Causes of the Mexican War.] [Sidenote: Texas.] It was during the term of President John Tyler, who succeeded to the chief magistracy after poor worn-out old General Harrison had exercised its functions for one brief month, that the events took their rise which ripened into the War with Mexico. The large territory of Texas, lying upon our extreme southwestern border, between Louisiana and Mexico, had revolted from the latter nation and set up an independent republic of its own. Texas had been largely colonized from the slave States, and General Sam Houston, formerly of Tennessee, was its President. [Sidenote: Election of Polk.] The republic sought admission to our Union in 1837, but the application was then refused. Seven years later, Mr. Tyler gave it a more hospitable reception. A treaty was framed, and at first rejected by the United States Senate. At last, in March, 1845, just as Mr. Tyler was retiring from office, a resolution was adopted by both houses of Congress annexing Texas, and this resolution was approved by the outgoing President. The presidential campaign in the autumn of 1844, between Henry Clay as the Whig and James K. Polk as the Democratic candidate, was fought mainly upon the issue of this annexation, and the election of Mr. Polk was looked upon as a confirmation of it by the people. [Sidenote: Boundary Dispute.] No sooner had the new President been inaugurated than what the Whig leaders had earnestly predicted came to pass. A dispute arose with Mexico as to the boundary between that country and Texas. Mexico claimed that this boundary was the river Nueces; Texas asserted it to be the Rio Grande. The matter was one of some importance, as the Nueces is a hundred miles northeastward from the Rio Grande, and that much of territory was therefore in dispute. The brief negotiations which ensued with a view to the settlement of this question, proved abortive. President Polk accordingly ordered General Zachary Taylor to occupy the disputed territory with a small body of troops. Taylor concentrated his men at Corpus Christi, near the frontier. [Sidenote: First Battles.]