When the history of 2014 is written, it will take note of a large fact that has received little attention: 2014 was the last year in which the United States could claim to be the world’s largest economic power. China enters 2015 in the top position, where it will likely remain for a very long time, if not forever. In doing so, it returns to the position it held through most of human history.

Comparing the gross domestic product of different economies is very difficult. Technical committees come up with estimates, based on the best judgments possible, of what are called “purchasing-power parities,” which enable the comparison of incomes in various countries. These shouldn’t be taken as precise numbers, but they do provide a good basis for assessing the relative size of different economies. Early in 2014, the body that conducts these international assessments—the World Bank’s International Comparison Program—came out with new numbers. (The complexity of the task is such that there have been only three reports in 20 years.) The latest assessment, released last spring, was more contentious and, in some ways, more momentous than those in previous years. It was more contentious precisely because it was more momentous: the new numbers showed that China would become the world’s largest economy far sooner than anyone had expected—it was on track to do so before the end of 2014.

The source of contention would surprise many Americans, and it says a lot about the differences between China and the U.S.—and about the dangers of projecting onto the Chinese some of our own attitudes. Americans want very much to be No. 1—we enjoy having that status. In contrast, China is not so eager. According to some reports, the Chinese participants even threatened to walk out of the technical discussions. For one thing, China did not want to stick its head above the parapet—being No. 1 comes with a cost. It means paying more to support international bodies such as the United Nations. It could bring pressure to take an enlightened leadership role on issues such as climate change. It might very well prompt ordinary Chinese to wonder if more of the country’s wealth should be spent on them. (The news about China’s change in status was in fact blacked out at home.) There was one more concern, and it was a big one: China understands full well America’s psychological preoccupation with being No. 1—and was deeply worried about what our reaction would be when we no longer were.

Of course, in many ways—for instance, in terms of exports and household savings—China long ago surpassed the United States. With savings and investment making up close to 50 percent of G.D.P., the Chinese worry about having too much savings, just as Americans worry about having too little. In other areas, such as manufacturing, the Chinese overtook the U.S. only within the past several years. They still trail America when it comes to the number of patents awarded, but they are closing the gap.

The areas where the United States remains competitive with China are not always ones we’d most want to call attention to. The two countries have comparable levels of inequality. (Ours is the highest in the developed world.) China outpaces America in the number of people executed every year, but the U.S. is far ahead when it comes to the proportion of the population in prison (more than 700 per 100,000 people). China overtook the U.S. in 2007 as the world’s largest polluter, by total volume, though on a per capita basis we continue to hold the lead. The United States remains the largest military power, spending more on our armed forces than the next top 10 nations combined (not that we have always used our military power wisely). But the bedrock strength of the U.S. has always rested less on hard military power than on “soft power,” most notably its economic influence. That is an essential point to remember.