The year I moved away, George W. Bush stood beneath a “Mission Accomplished” banner on an aircraft carrier and declared an end to major combat operations in Iraq. Facebook hadn’t yet been turned into a company. The iPhone did not exist. I left before Hurricane Katrina devastated New Orleans, before Detroit went bankrupt. I missed the Great Recession (though I am still living the European translation of it). I missed most of the last two presidencies. I missed Brangelina.

Instead, I witnessed from the other side the global forces that would bring profound changes to America. I visited industrial regions of southern China where the ground seemed to vibrate under the weight and bustle of all the countless new factories. Once iPhones had been invented, it was Chinese workers who assembled them. I watched Bangladeshi seamstresses stitch clothes sold at Walmart. American consumers benefited from the cheaper goods, but American manufacturers did not. Between January 2000 and December 2014, the United States lost roughly five million manufacturing jobs.

Then I moved to Rome and watched the European Union grow ineffective and paralyzed, as the dream of a vibrant, unified Europe seemed to wither. Democracy was losing ground in Hungary and the Philippines; it had all but surrendered in Russia. Syria became a slaughterhouse. The Islamic State dispatched terrorists around the world. China’s politics became more oppressive, as President Xi Jinping cracked down on dissent and nurtured a Maoist-style cult of personality. Economic globalization was supposed to accelerate political liberalization around the world, but instead authoritarianism appeared to be on the rise. The West, it seemed, had failed to anticipate the possibility that globalization could contribute to the destabilization of — or pose a threat to — democracy, even in the United States.

This summer, I decided I wanted to explore this place that had become a foreign country to me. I didn’t understand what had happened since I left, why so many people seemed so disillusioned and angry. I planned a zigzag route, revisiting places where I once lived or worked, a 29-day sprint through 11 states (and four time zones). I knew I would be moving too fast to make any sweeping declaration about the state of America, and I wouldn’t ask people which presidential candidate they were voting for. I was more interested in why they were so anxious about the present and the future. I wanted to find out why the country was fragmenting rather than binding together. Most of all I wanted to see with my own eyes what had changed — and so much had changed.

By the time I arrived in Washington in late July, the notion that American democracy could come unmoored was not being easily laughed off. Before beginning my journey in earnest, I paid a visit to Patrick J. Buchanan at his white mansion near the headquarters of the Central Intelligence Agency in Northern Virginia. I’d thought of Buchanan often over the last year, as Donald Trump secured the Republican nomination. In 1992, I covered Buchanan during a campaign stop in Macomb County, outside Detroit, when he was a Republican insurgent running for president, the Trump of that era. He mocked Republican elites, denounced free trade and globalization, antagonized minorities and vowed to build a “Buchanan fence” along the Mexican border. Buchanan’s nostalgia for the era of white-majority America was often interpreted, not without cause, as barely concealed racism. He lost in 1992, and again in 1996 and 2000, but he always predicted that his issues and his angry coalition would endure.