Before Polk, the United States and Mexico had boundaries along the Rio Grande River. Texas and Polk claimed that America's southern border ran down to the river south of the United States' positon back then. They had a war, but Mexico lost and U.S kept expanding. Hope this helps!
Answer: it's California
Before Polk's term, the Rio Grande was recognized as the border, while Texas claimed the Nueces River. Polk chose the Rio Grande, which prompted conflict with Mexico. The U.S. military presence in disputed territory fueled tensions, leading to the Mexican-American War.
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