This is not a G-20 world. Over the past several months, the expanded group of leading economies has gone from a would-be concert of nations to a cacophony of competing voices as the urgency of the financial crisis has waned and the diversity of political and economic values within the group has asserted itself. Nor is there a viable G-2 -- a U.S.-Chinese solution for pressing transnational problems -- because Beijing has no interest in accepting the burdens that come with international leadership. Nor is there a G-3 alternative, a grouping of the United States, Europe, and Japan