It is difficult to find a westerner who does not intuitively support the idea of a free Tibet. But would Americans ever let go of Texas or California? For China, the Anglo-Russian great game for control of central Asia was neither inconclusive nor fruitless, something that cannot be said for Russia or Britain. Indeed, China was the big winner.

Boundary agreements in 1895 and 1907 gave Russia the Pamir mountains and established the Wakhan Corridor - the slender eastern tongue of Afghanistan that borders China - as a buffer to Britain. But rather than cede East Turkestan (Uighurstan) to the Russians, the British financed China's recapture of the territory, which it organised into Xinjiang (which means "New Dominions"). While West Turkestan was splintered into the hermetic Soviet Stans, China reasserted its traditional dominance over Xinjiang and Tibet, today its largest - and least stable - provinces. (Beijing has now accused the Dalai Lama of colluding with Muslim Uighur separatists in Xinjiang.) But without them, the country would be like America without all territory west of the Rockies: denied its continental majesty and status.

Every backpacker who has visited Tibet and Xinjiang in the past decade knows that the Chinese empire is painfully real: the western region's going concern is undoubtedly Chinese Manifest Destiny. With the end of the civil war in 1949, China endeavoured immediately to overcome the "tyranny of terrain" and tame the interminable mountain and desert landscapes with the aim of exploiting vast natural assets, establishing penal colonies and military bases, and expand the Lebensraum for its exploding population.

Both Tibet and Xinjiang have the misfortune of possessing resources China wants and of being situated on the path to resources China needs: Tibet has vast amounts of timber, uranium and gold, and the two territories constitute China's geographic gateway for trade flow outward - and energy flow inward - with Kazakhstan, Kyrgyzstan, Tajikistan, Afghanistan and Pakistan.

Decades of labour by the army and swarms of workers have paved the way for unchallenged Chinese dominance. The high-altitude train linking Shanghai and Lhasa that began service in 2006 represents not the beginning of Chinese hegemony, but its culmination.

Tibet and Xinjiang today set the stage for the birth of a multi-ethnic empire in ways that resemble nothing so much as America's frontier expansion nearly two centuries ago. Chinese think about their mission civilatrice much as American settlers did: they are bringing development and modernity. Asiatic, Buddhist Tibetans and Turkic, Muslim Uighurs are being lifted out of the third world - whether they like it or not.

They are getting roads, telephone lines, hospitals and jobs. School fees are being reduced or abolished to promote basic education and Chineseness. Unlike those Europeans who seek to define the EU as a Christian club, there are no Chinese inhibitions about incorporating Muslim territories. The new mythology of Chinese nationalism is based not on expunging minorities but granting them a common status in the paternalistic state: Uighurs and Tibetans, though not Han, are told they are Chinese.

"The Soviet Union collapsed because they experimented with glasnost prematurely, before the achieved unity among the peoples," explains a Chinese intellectual in Shanghai who studies central Asia. Large empires are maintained through a combination of force and law; and as recent weeks illustrate, China is determined not to waver.

In even the remotest corners of Tibet, small bases house platoons of the People's Liberation Army, with soldiers menacingly practising martial arts twice daily in public squares, often right next to ancient Buddhist stupas. Inaccessible jungle areas designated environmentally protected zones are often actually military encampments. Signs trumpeting "Tibet power" refer strictly to the Chinese electricity company.

China has pumped in billions of development dollars, hoping to generate goodwill among the scarcely 3 million Tibetans. In Lhasa, crumbling stone quarters have been replaced with sturdy homes built along thoroughfares connecting the city to the new railway station. The consequence of Chinese modernity, however, is that a city that once symbolised cultural authenticity has become merely a gateway to the remote plateaus where wild yak still outnumber people.

An even greater prize than Tibet is the far larger and more populous Xinjiang, with its oil deposits, deserts and mountains. Its demographic dilution has been dubbed "apartheid with Chinese characteristics". Xinjiang's Muslims have always been unruly, even briefly securing an independent East Turkestan at the end of the civil war. But massive Han resettlement began with the "Develop the west" campaign of the 1950s, and in the cultural revolution Xinjiang was sealed off for a massive pogrom of mosque destruction and Qur'an burning. Violent clashes in Urumqi, Xinjiang's capital, in 1996 proved that no peaceful Islamic culture would prevail in a Chinese-dominated environment. China suspended all mosque reconstruction and launched a "Strike Hard" campaign, imprisoning and executing hundreds of suspected separatists. Today one can see the results of a programme Mao and Deng began, but never completed: a railway and highway transporting coal, migrants and goods across the Taklamakan desert, facilitating the Hanification of a province where Uighurs now make up only half the population.

The annihilation of local people, history and architecture, and their replacement with shiny skyscrapers paying tribute to modern Chinese capitalism, make Urumqi the Shanghai of the northern Silk Road. A six-lane freeway runs through the city, and the Han majority fill up spiffy Japanese cars at the large Sinopec and PetroChina petrol stations. Urumqui buzzes with traders from Russia to Pakistan and all Stans in between, who buy cheap Chinese goods to be sold back home at a profit. Uighurs are now a marginalised minority in the city. Chinese tourists crowd the few accessible natural attractions, making the emerald-coloured Heavenly Lake no longer very heavenly.

Ironically, China's near absolute sense of security over both provinces is the greatest hope for a Chinese glasnost: China no longer faces any meaningful resistance to its rule and so some day may lighten up. Spiritual Tibetans have long looked south to Nepal and India for their cultural underpinnings, and in the 18th century Tibet was allowed a functional autonomy from China, a model the current Dalai Lama has proposed. Once he passes the scene, China might be less anxious about cultural exchange between Buddhists, further restoring Tibet's role as the Silk Road passage it was when Dunhuang's Caves of the Thousand Buddhas were carved, more than a millennium ago.

Tibetans and Uighurs will gradually become more prosperous than their neighbouring Mongols, Kyrgyz, Tajiks, Afghans, Pakistanis, Indians, and Nepalis - and this may provide a basis for Chinese claims of a benevolent hegemony elsewhere in Asia. But China will achieve that dominance before it talks about it.

· This is an edited extract from Parag Khanna's book The Second World: Empires and Influences in the New Global Order, which will be published next week

paragkhanna.com