Final answer:
President Polk said he sent troops into the disputed territory in Texas because he believed Mexico had invaded U.S. land and shed American blood upon American soil.
Step-by-step explanation:
President Polk said he had sent troops into the disputed territory in Texas because he believed that Mexico had invaded U.S. land and shed American blood upon American soil. He declared war on Mexico, claiming that he had exhausted all efforts at reconciliation. Mexico, on the other hand, contended that the United States had not only taken Texas but also tried to double its size. The border dispute and conflicting perceptions ultimately led to the outbreak of war.