In June 1845, President James K. Polk sent General Zachary Taylor to Texas, and by October, 3,500 Americans were on the Nueces River, prepared to defend Texas from a Mexican invasion. On November 10, 1845, Polk ordered General Taylor and his forces south to the Rio Grande, into disputed territory that Mexicans claimed as their own. Mexico claimed the Nueces River—about north of the Rio Grande—as its border with Texas. On April 25, 1846, a 2,000-strong Mexican cavalry detachment attacked a 70-man U.S. patrol that had been sent into the contested territory north of the Rio Grande and south of the Nueces River. The Mexican cavalry routed the patrol, killing 16 U.S. soldiers in what later became known as the Thornton Affair. Both nations declared war. In the ensuing Mexican–American War, there were no more battles fought in Texas, but it became a major staging point for the American invasion of northern Mexico. One of the primary motivations for annexation was the Texas government's huge debts. The United States agreed to assume many of these upon annexation. However, the former Republic never fully paid off its debt until the Compromise of 1850. In return for $10 million, a large portion of Texas-claimed territory, now parts of Colorado, Kansas, Oklahoma, New Mexico, and Wyoming, was ceded to the Federal government. Intensified migration to Texas after statehood raised the population to about 150,000. Societies such as the Texas Emigration and Land Company now pledged to settle colonists who would agree to constitute a militia for defense against the Indians; in return they would receive a grant of 320 acres of choice land. Most of the newcomers continued to migrate from the states of the lower South; slavery was granted legal protection by the Texas constitution of 1845. The Texas population by 1860 was quite diverse, with large elements of European whites (from the American South), African Americans (mostly slaves brought from the east), Tejanos (Hispanics with Spanish heritage), and about 20,000 recent German immigrants. The new state grew rapidly as migrants poured into the fertile cotton lands of east Texas. With their investments in cotton lands and slaves, Texas planters established cotton plantations in the eastern districts. The central area of the state was developed more by subsistence farmers who seldom owned slaves. Texas in its Wild West days attracted men who could shoot straight and possessed the zest for adventure, "for masculine renown, patriotic service, martial glory and meaningful deaths."