"Superfusion" — that’s the name of a new book by Zachary Karabell, which describes how "the unique relationship between China and the United States has become the axis of the world economy." It’s a catchy concept in a world that struggles to find the terms to keep pace with a rapidly changing economy. It’s pretty much identical to another neologism, coined a couple of years ago by the economic historians Niall Ferguson and Moritz Schularick to describe the Sino-American economic relationship. That one was Chimerica.

Americans are born with the consumption gene, and borrow, not earn, their way to the American dream of home and business ownership. Chinese, on the other hand, have the thrift ethos drummed into them from birth. Their Government has continued to pour money into investment in infrastructure and industry for export to drive growth and raise living standards. But the Chinese Government has not built the kind of social safety net and retail financial system that would lead its citizens to save less, consume more and build a vibrant and sustainable domestic market-led model of economic development. Whether they like it or not, China and the US will be stuck with Chimerica for a long time.

The defining feature of the current world economy is not an excess of liquidity or a shortage of assets, but the gap between company profits and the level of real interest rates. This wedge between the return on capital and the cost of capital is in large measure attributable to the spectacular rise of what we call "Chimerica": the sum of China, the world's most rapidly growing emerging market, and America, the world's most financially advanced developed economy.