of Texas. This border dispute between the newly expanded United States and Mexico triggered the Mexican–American War. When the war concluded, Mexico relinquished its claim on Texas, as well as other regions in what is now the southwestern United States. Texas' annexation as a state that tolerated slavery had caused tension in the United States among slave states and those that did not allow slavery. The tension was partially defused with the Compromise of 1850, in which Texas ceded some of its territory to the federal government to become non-slave-owning areas but gained El Paso. Mexican–American War American territorial expansion to the Pacific coast was a major goal of U.S. President James K. Polk. In 1845, the United States of America annexed Texas, which had won independence from Centralist Republic of Mexico in the Texas Revolution of 1836. Mexico did not accept the annexation, while also continuing to claim the Nueces River as its border with Texas, and also still considering Texas to be a province of Mexico. In 1845, newly elected U.S. President James K. Polk sent troops to the disputed area, and a diplomatic mission to Mexico. After Mexican forces attacked American forces, the U.S. declared the Mexican–American War (1846–1848). Combat operations lasted a year and a half, from the spring of 1846 to the fall of 1847. U.S. forces quickly occupied the capital town of Santa Fe de Nuevo México along the upper Rio Grande and began the Conquest of California in Mexico's Alta California Department. They then invaded to the south into parts of central Mexico (modern-day northeastern Mexico and northwest Mexico). Meanwhile, the Pacific Squadron of the United States Navy conducted a blockade and took control of several garrisons on the Pacific coast farther south in lower Baja California Territory. The U.S. Army eventually captured the capital Mexico City, having marched west from the port of Veracruz, where the Americans staged their first amphibious landing on the Gulf of Mexico coast. The 1848 Treaty of Guadalupe Hidalgo, forced onto the remnant Mexican government, ended the war and specified its major consequence, the Mexican Cession of the northern territories of Alta California and Santa Fe de Nuevo México to the United States. The U.S. agreed to pay $15 million compensation for the physical damage of the war. In addition, the United States assumed $3.25 million of debt already owed earlier by the Mexican government to U.S.