From poets to sociologists, many people who write about life on the U.S.-Mexico border use terms such as "border crossing" and "hybridity" which suggest that a unified culture-neither Mexican nor American, but an amalgamation of both-has arisen in the borderlands. But talking to people who actually live on either side of the border reveals no single commonly shared sense of identity, as Pablo Vila demonstrated in his book Crossing Borders, Reinforcing...