James K. Polk
Annotation: In this document, President James K. Polk instructs his minister to Mexico, John Slidell, to insist that the Rio Grande be Texas’s southern boundary.
Document: In regard to the right of Texas to the boundary of the del Norte [Rio Grande River]…there cannot, it is apprehended, be any very serious doubt. It would be easy to establish, by the authority of our most eminent statement—at a time, too when the question of the boundary of the province of Louisiana was better understood than it is at present--…the del Norte was its western limit…. It cannot be denied, however, that the Florida treaty of 22d February, 1819, ceded to Spain all that part of ancient Louisiana within the present limits of Texas; and the more important inquiry now is, what is the extent of the territorial rights which Texas has acquired by the sword in a righteous resistance to Mexico. In your negotiations with Mexico, the independence of Texas must be considered a settled fact, and is not to be called in question…. Should the Mexican authorities prove unwilling to extend our boundary beyond the del Norte, you are, in that event, instructed to offer to assume the payment of all the just claims of citizens of the United States against Mexico, should she agree that the line shall be established along the boundary defined by the act of Congress of Texas approved December 19, 1836….