sentences:  The aspect of Spanish-American relations that would bear most prominently on later relations between the U.S. and Mexico was the ownership of Texas.In the early 19th century the United States claimed that Texas was part of the territory of Louisiana, and therefore had been rightfully acquired by the United States as part of the Louisiana Purchase from France in 1803.The Spanish, however, claimed it was not, as the western boundaries of Louisiana were not clearly defined.