The current world tour by Mexico's President Luis Echeverria produced a modest but unexpected diplomatic bonus last week. During Echeverria's visit in Paris, President Georges Pompidou announced that France would associate itself with the Treaty of Tlatelolco, a pact signed in 1967 by 21 Caribbean and Latin American nations (not including Cuba) to bar all nuclear weapons in the region from Mexico to Tierra del Fuego.
Britain ratified a separate protocol in 1969, pledging not to use or threaten to use nuclear weapons in the treaty territory; the U.S. ratified the same protocol in...