<P> During the late - 1830s and early - 1840s , the river marked the disputed border between Mexico and the nascent Republic of Texas ; Mexico marked the border at the Nueces River . The disagreement provided part of the rationale for the US invasion of Mexico in 1846 , after Texas had been admitted as a new state . Since 1848 , the Rio Grande has marked the boundary between Mexico and the United States from the twin cities of El Paso , Texas , and Ciudad Juárez , Chihuahua , to the Gulf of Mexico . As such , crossing the river was the escape route used by some Texan slaves to seek freedom . Mexico had liberal colonization policies and had abolished slavery in 1828 . </P>
<P> During the late - 1830s and early - 1840s , the river marked the disputed border between Mexico and the nascent Republic of Texas ; Mexico marked the border at the Nueces River . The disagreement provided part of the rationale for the US invasion of Mexico in 1846 , after Texas had been admitted as a new state . Since 1848 , the Rio Grande has marked the boundary between Mexico and the United States from the twin cities of El Paso , Texas , and Ciudad Juárez , Chihuahua , to the Gulf of Mexico . As such , crossing the river was the escape route used by some Texan slaves to seek freedom . Mexico had liberal colonization policies and had abolished slavery in 1828 . </P>
the part of mexico north of the rio grande used to be called
the part of mexico north of the rio grande used to be called
Republic of Texas
Republic of Texas