Xinjiang, in the far western land of China, hosted one of the world's first and most important trade routes known as the Silk Road, which linked ancient Chinese civilization to the West through the Eurasian continent.

The land of fortune, however, has not always enjoyed tranquility. Thousands of terrorist attacks from 1990 through 2016 killed large numbers of innocent people and hundreds of police officers. Horrific stabbings and bombings wrecked the land, leaving its people in shock, grief and panic. The damage was incalculable while stability in the region quickly deteriorated. Authorities have been trying hard to restore peace to this land.

In CGTN's first three documentaries on fighting terrorism in Xinjiang, we presented never-before-seen footage documenting the frightening tragedies in Xinjiang and the resilience of its people.

The fourth exposé "The war in the shadows: Challenges of fighting terrorism in Xinjiang" – the last of the tetralogy – exposes the extremist thinking and the challenges facing China's efforts to tackle terrorism inside and outside Xinjiang.

It gives answers to these questions: Why has violent terrorism continued to plague Xinjiang? For those who were once known as "Two-faced people" among the legal and political elites in Xinjiang, how much damage have they done to anti-terrorism efforts in the region? How come poisonous education materials alleging ethnic victimization and "Turkic heroes" have been used for 13 years in primary and middle schools? Why must we stop the invisible hand of foreign advocacy abetting violent terrorism infiltrating our country?

The documentary reveals the methods used by extremist and separatist forces including the "Two-faced people" among the region's high-ranking officials, as well as how music and videos advocating violent terrorism and inciting ethnic hatred penetrated the region. Plus, it also tells of the very hardship police officers have been mired in for decades.

Over the past four years, violence has largely been contained, giving way to rapid urbanization and economic growth. Safety and tranquility never come easy. But it's only a preliminary victory in China's fight against terrorism.

The documentary is 55 minutes long and consists of four parts: "The network," "Enemies within," "The textbooks," and "The black hands."

We present you with the first three documentaries — each under an hour — below.

Watch: Fighting terrorism in Xinjiang

Watch: The black hand — ETIM and terrorism in Xinjiang

Watch: Tianshan: Still standing – Memories of fighting terrorism in Xinjiang