BEIJING, China — When North Korea tested its nuclear weapons last year, the people of Yanji, China, felt an earthquake.

When civil wars tore apart a section of northeast Myanmar, small towns in southern Yunnan flooded with tens of thousands of frightened Burmese refugees.

When demonstrations by China’s Muslim Uighurs erupted into deadly riots that underscored the depth of ethnic tensions, new questions arose about China’s policies of cultural assimilation and controls on the practice of Islam and other religions.

In short, China’s most delicate and dicey challenges are often seen most dramatically on its borders. In the regions where China meets the rest of the world, its own ethnic lines are blurred by intense concentrations of minority populations, sometimes dominating whole provinces like Xinjiang, Tibet, Inner Mongolia and Manchuria. Many of these regions have broken away from Chinese control throughout history. Today the borders are strong, but the 14 countries that frame China couldn’t be more different, from Pakistan to North Korea and Mongolia to Myanmar.

It’s no small challenge for China, which, with 13,743 miles of international borders, has more borderlands than any other country in the world.

On the borders, the notion and appearance of a uniform Chinese people and culture fades away. Diversity flourishes, from religion and architecture to language, politics and resources. A common thread in every border region is an underlying tension between local ethnicities and the dominant Han Chinese culture, which makes new inroads into border regions each year.

China’s interior and eastern seaboard are dominated by economic growth the likes of which the world has never seen. But in its furthest north, west and south reaches lie perhaps the most fascinating parts of the country.

There is the tightly controlled North Korean border, where armed soldiers on both sides of the line patrol with marked tension, looking for unwelcome refugees. The fluid border with Myanmar, where Chinese and Burmese cross back and forth with ease and open smuggling is a 24-hour reality. The old Silk Road oasis of Kashgar, set within a stone's throw of multiple heated global conflict areas, including Kashmir, Pakistan and Afghanistan. And Guangzhou, where many of the plants and animals smuggled across China's borders end up for sale.

Each border region has common challenges, often handled differently depending on location. Based on dozens of interviews and thousands of miles of travel, this GlobalPost series "Borderland" explores how China deals with its neighbors, and what life is like on China’s boundaries. We’ve looked at trafficking, religion, history, trade and environmental issues.

“Every border area is quite different than the rest of the country, and every border area is different from the other,” said Li Guogang, deputy director of the Chinese Academy of Social Sciences Center for China’s Borderland History and Geography Studies — a government affiliated institute that researches and advises on border policy.

Li, who specializes in North Korean border policy, said the vast differences are not due to any discrepancies in Chinese policy. Instead, he argues, cultural and environmental conditions differ across the country. China has a single border policy, he says, and it’s quite simple: stability.

“If the borders in China are not stable, all of China will be unstable. If the border areas are not developed, all of China will be undeveloped,” Li said, citing what he says is old government wisdom. “We can say the border areas are extremely important, throughout history.”

By looking at border issues through the eyes of a prostitute from Myanmar, a Chinese businessman trading with North Korea, Muslim Uighur teenagers and others, "Borderland" seeks to better explain China’s contrasts and challenges by starting on its frontiers.

As you will see, read and hear — it's quite a journey.