Between 1830 and 1845 there was a war to decide the boundaries of Texas. Americans thought that the border should be at Rio Grande. While the Mexicans didn't want the line to go past the Nueces River. After a few battles the Mexicans were driven back past the Rio Grande line. But the Mexicans would not make peace. In Rio Grande, General Taylor took up a strong position at Buena Vista. The Mexicans attacked him with roughly 20,000 warriors. General Taylor's small army fought for their lives for two days straight and ended up with a very important victory.