G-Zero — \JEE-ZEER-oh\ —n A world order in which no single country or durable alliance of countries can meet the challenges of global leadership. What happens when the G20 doesn’t work and the G7 is history.   If the worst threatened—a rogue nuclear state, a major health crisis, the collapse of the global financial system—where would the world look for leadership?   For the first time in seven decades, there is no single power or alliance of powers ready to take on the challenges of global leadership. A generation ago, the United States, Europe, and Japan were the world’s powerhouses, the free-market democra­cies that propelled the global economy forward. But today, they struggle just to find their footing.   Acclaimed geopolitical analyst Ian Bremmer argues that this leadership vacuum is here to stay, as power is regionalized instead of globalized. Now that so many challenges transcend borders—from the stability of the global economy and climate change to cyber-attacks and terrorism—the need for international cooperation has never been greater.