Mexico, in the meantime, had offered to recognize the independence of Texas and to make peace with her if the Texas Congress would reject the joint resolution, and refuse the proffered annexation. This the Texas Congress refused, and with the passage, by that body, of an act providing for annexation, the Mexican minister was withdrawn from Washington, and Mexico began her preparations for war. President Polk had taken office with the avowed intention of buying California from Mexico. The rupture threatened to prevent him from carrying this plan into effect. He therefore sent an unofficial representative to Mexico in an effort to restore friendly relations. Failing in that, he and his advisers determined upon war as the only feasible method of obtaining California and of settling the diplomatic tangle involved in the annexation of Texas. 4. _The Conquest of Mexico_ The Polk Administration made the Mexican War as a part of its expansionist policy. "Although that unfortunate country (Mexico) had officially notified the United States that the annexation of Texas would be treated as a cause of war, so constant were the internal quarrels in Mexico that open hostilities would have been avoided had the conduct of the Administration been more honorable. That was the opinion of Webster, Clay, Calhoun, Benton, and Tyler.... Mexico was actually goaded on to war. The principle of the manifest destiny of this country was invoked as a reason for the attempt to add to our territory at the expense of Mexico."[29] After the annexation of Texas it became the duty of the United States to defend that state against the threatened Mexican invasion. Mexican troops had occupied the southern bank of the Rio Grande. General Zachary Taylor with a small force, moved to a position on the Nueces River. Between the two rivers lay a strip of territory the possession of which was one of the sources of dispute between Mexico and Texas. What followed may be stated in the words of one of the officers who participated in the expedition: "The presence of the United States troops on the edge of the territory farthest from the Mexican settlements was not sufficient to provoke hostilities. We were sent to provoke a fight, but it was essential that Mexico begin it" (p. 41). "Mexico showing no willingness to come to the Nueces to drive the invaders from her soil, it became necessary for the 'invaders' to approach to within a convenient distance to be struck. Accordingly, preparations were begun for moving the army to the Rio Grande, to a point near Matamoras. It was desirable to occupy a position near the largest center of population possible to reach without actually invading territory to which we set up no claim whatever" (p. 45).[30]