Ian Bremmer, author of 'Every Nation For Itself: Winners and Losers in a G-Zero World'

It began with a cozy cabal, the G-6. Then along came Russia and Canada, and the G-8 became the new word in global summitry. Now leadership summits have become super-sized, with the G-20 now the one-stop shop for tackling the world's most pressing problems. Except that these days neither G20s, nor G8s, nor G-Anythings, really tackle much at all, according to our guest, Ian Bremmer.