(a) The period of stalemate between Tang and Tibet (641--755)

From Tang Tai-Chung to Tang Min-Huang, there was a stalemate in the military relations between those two kingdoms. There were very few conflicts during the time of Tang Tai-Chung and Srong-tsan-gam-po (Songtsen Gampo). The next Emperor of Tang decided to move Tu-Yu Huen back to its original territory in the southern part of Qinghai (Amdo in Tibetan). The conqueror of Korea, General Hsueh Zen-Kuei, was given a title of `Governor of Lhasa' and led an army of 100,000 strong for this assignment. When his army reached the high plateau of Qinghai, a Tibetan army of 400,000 strong appeared and swept the Tang army away. Then the Tibetan army marched to the southern Xinkiang and captured the four Tang garrisons. Later, General Wang Xiao-Jia recaptures the four Tang garrisons and pushed on to attack the high plateau of Qinghai, and met his defeat there.

During this period, there were expansions for Tang and Tibet. Tang's imperial army conquered Turks, Korean, Xinkiang, Central Asia (part of the formal Soviet Union) reached all the way to Persia. In fact, once Tang had a garrison in the capital of Persia. Tibet conquered the kingdoms Shangshung, Greater Yang-Tuung, Lesser Yang-Tung, Su-pi of Tibet, and Tu-yu Huen and all small tribes in Qinghai.

At the end of this period, Tang had a population of 52 millions (increased from 15 millions, and the total population of Euro-Asia-Northern Africa was about 150 millions at that time) and an imperial army of 490,000 strong which was divided into garrisons of Mongolia, Northeast Tang, Northern Xinkiang, Southern Xinkiang (including Central Asia) and the Silk-road (Gansu) (including the fertile corner of Qinghai). Tibet had a population of 10 million with 3 million Tibetans (all estimates) and an army of comparable strength facing the two Tang army of Southern Xinkiang (24,000 soldiers) and Silk-road (75,000 soldiers).

The disputes involed trade contrals. Tibet wanted the four Tang garrisons at the Southern Xinkiang (which guarded the silk-road from Tang through Xinkiang and Central Asia), and Tang wanted the re-establishment of Tu-Yu Huen as the power in Qinghai (most Tu-Yu Huen moved back to the valleys at the source of Yellow river and were called `Atsai' in Tibetan). Otherwise the relations between them were close and cordial. For instance, when an ambassador of Tang to India, Mr. Wang, was in trouble, he went to Tibet and was given an army to ransack the capital of a kingdom of India. The ambassador brought back, besided others, an Indian expert of making `immortal medicine'. The great Tang Tai-Chung ate the immortal medicine and passed away. The Tang court thought the whole event was embarrassing and hid the truth.

(b) The weakening of Tang and the expansion of Tibet (755--841)

In 755, the commander of the Northeast garrison of Tang, An Lu-San (Mongol) rebelled. He led an army of 150,000 strong marched to the capital. The public opinion of the capital was condescending. Most people thought the rebellion were a joke.

A good general Fon Chang-Jin (possibly a native from a tribe of Southern Xinkiang, Conqueror of Da-Bo-Lu, i.e., Gilgit) agreed with the public opinion and was ordered by the Emperor to lead the totally untrained garrison of Loyang to face An Lu-San's army. A famous Korea general Guo Xieng-Ze (Victor of Central Asia and the loser of a war with Persia) led the palace guards and a portion of the Silk-road (Gansu) army as the second wave. General Fon, when met General Guo (a friend and formal superior of General Fon), told General Guo that An Lu-San's army was surprisingly strong, and the fact that after a blooded continuous battle of 50 km, Gen Fon was forced to withdraw, and the only way to protect the capital was to guard the castle area (Tong-Kuan). Through good military sense, General Guo did accordingly and took a defense posture at the castle area. An Lu-San's army was stopped. The Emperor Min-Huang was impatient and was moved by the public opinion. He sent someone to kill the two generals. In the meantime, the Silk-road army and the best troops from the garrisons of Northern and Southern Xinkiang were called back to protect the capital. The Emperor sent the famous Turk General Gow-Su Han to lead the army at hand. The old General saw the situation himself and decided to defend from the castles to wait for the gathering of all imperial garrisons from distances. Emperor Min-Huang did not want anything like that. He sent a strict order to attack An Lu-San's army. The old General wept openly and obeyed the order and was captured by An Lu-San's army.

The war lasted until 763 after Tang court adapted a strategy of dividing the whole Tang into `military zones' (similar to what Mao did in the CR, after the victory over An Lu-San, the `military zones' became semi-independent and brought down the Tang dynasty, Mao switched the policy just in time to avoid a repetition of history), and An Lu-San's army was squeezed and bled to death eventually.

After the withdrawing of the Silk-road army and the passaging of the best troops from the garrisons of Northern and Southern Xinkiang, Tibetan army swept through and captured the Silk-road which was the richest part of Tang at that time. Thus Tibet bordered Hue-He (Mongol) and cut off Silk-road completely. The residues of the Northern and Southern garrisons of Xinkiang organized successive defenses and lasted many decades. During the time, they were waiting for the imperial army to re-open the Silk-road. After some 10 years, they sent a messenger through Mongolia to report to the imperial court. Finally, Northern garrison of Xinkiang was eliminated (790) after all old soldiers faded away, and Southern garrison disappeared into the murky history. Later on, during the conquering of Mongolia Genghis Khan, some Han tribes in the central Asia were mentioned. They were likely to be the descendents of the Southern Xinkiang garrison (which covered the central Asia).

Years later, after the downfall of Tibetan Dynasty, Tang recovered Silk-road (848). This story will be discussed later in this article.

In the mean time, Tibet attacked Szechuan and fought many inconclusive battles with Tang army. The part Yunnan of Tang rebelled and established a local kingdom. First, Yunnan got the protection from Tibet by being a tributary of Tibet. Later on Tang recognized Yunnan, and Yunnan switched side and became a tributary of Tang.

Sometimes the Tibetan army became mercenaries of Tang to fight with several rebels. Other time, the Tibetan army simply attacked Tang. Once Tibetan army ransacked the capital of Tang and crowned a new Emperor who lasted for a few days (763).

Just before the downfall of Tibetan Dynasty, Tibetan governed Tibet, Qinghai, Silk-road, part of southern Xinkiang, part of central Asia. Tibet bordered with India, Tang, Persia, Mongolia. This was the largest area which was ever controlled by Tibetan. It had a population of 15 millions and an army of 400,000 strong (all estimates).

At that time, Tang had a population of 16 millions and an army of 150,000 strong.