Before Tongguan War, although An Lushan troops were on a roll and captured Luoyang in a short time, the situation was not one-sided, and Tang Jun still had the advantage in the war.

Guo Ziyi and Li Guangbi defeated Shi Siming one after another, cut off the connection between the Anshi Rebellion and john young's lair, and slowed down the rebel offensive. At the same time, An Lushan's fighting to the south and east met with great resistance. Tongguan, under the management of veteran Ge, was also impregnable and quite safe at that time.

Tongguan is easy to defend but difficult to attack, and it is the gateway to guard Guanzhong. If An Lushan's attack on Tongguan is frustrated, it will be caught between Scylla and Charybdis. This is very beneficial to the counter-insurgency in the Tang Dynasty. At this time, Feng Changqing and Gao Xianzhi retreated to Tongguan, determined to clear the field. Tang Jun has advantages in number and geographical location. As long as you stick to it, you can naturally drag it to An Lushan for withdrawing troops due to illness. It's a pity that a nobody changed this situation at this time and affected the whole war situation in the long run.

When Feng and Gao were stationed in Tongguan, Bian Lingcheng, an army supervisor, made several suggestions, but Gao Xianzhi didn't listen. Coupled with economic disputes, he bears a grudge and slanders Tang Xuanzong, saying that they deliberately gave their territory to thieves. Emperor Xuanzong of the Tang Dynasty was furious and ordered Bianling City to kill Gao Xianzhi and Feng Changqing in the army. There was no general in the army, and the rebels went straight to Chang 'an, and Tang Jun was defeated.

Even if Feng Hegao was killed, Tongguan still had a veteran Ge. Although Geshuhan's guards in Tongguan are old, weak and sick, using these forces to guard Guancheng is enough to deal with the rebels. But it is absolutely impossible for these troops to fight a decisive battle with An Lushan. As a result, Yang encouraged Tang Xuanzong to let Ge Shuhan go through the customs for a decisive battle, and the result was a fiasco. There were few troops left, and Tongguan finally fell.

To sum up, as long as Tang Xuanzong doesn't interfere, any one of them will survive, keep his own army and stop the rebels.