That has left us with a divide: Today, there is the Chinese internet, and there is the internet of the rest of the world. A network seen in its early days as a tool to foster financial and political unity across a fragmented planet has irrevocably cleaved into two completely separate spheres.

Mr. Kalanick, a famously competitive and aggressive entrepreneur, had apparently studied these risks and seemed determined to bridge that gulf. He would try to take on China not as an afterthought, but as a central mission of his fledgling company. He would risk billions and spend a great deal of time in China to figure out the secrets of winning there. The goal seemed lofty, but the opportunity, after all, was eye-popping: Amazon has a market value of $365 billion, and Alibaba is worth about $200 billion. The ride-hailing business might one day grow to be as valuable as e-commerce, if not larger — and wouldn’t it be fantastic if you could own it all, everywhere?

Well, you can’t. The announcement on Monday that Uber will sell its Chinese operations to its rival Didi Chuxing, effectively ceding China to the homegrown favorite, cements an emerging global state of play: A kind of Chinese-American Cold War over the internet.

Entrepreneurs across the globe can choose to win in China or the rest of the world. You can be Alibaba or you can be Amazon. You can be Uber or you can be Didi. But you can’t be both. Given the rising Chinese market and increasing tension over the role of American tech firms in the rest of the globe, the gulf between the two sides promises to become one of the most important factors in determining the shape of global tech innovation.

How exactly might the war play out? In some ways, being at the mercy of two poles of internet leadership could be good for citizens of planet Earth. In emerging markets like India, the Middle East and parts of Africa and South America, the giants of China and the United States are increasingly investing billions to compete for local customers in e-commerce, social networking, ride sharing and other markets.