Looking around a Mexico dotted by Starbucks, Wal-Mart and Krispy Kreme outlets, it's hard to remember the country before the North American Free Trade Agreement, which has dramatically expanded consumer choice and trade since it took effect 20 years ago on Jan. 1.

While it changed the country in some fundamental ways, the treaty never met many of its sweeping promises to close Mexico's wage gap with the United States, boost job growth, fight poverty and protect the environment. Mexico's weak unions and competition from Asia and Central America kept wages down; the tightening of security along the U.S. border closed off Mexico's immigration "escape valve," and environmental provisions in the agreement proved less powerful than those protecting investors.