In the early Tang Dynasty, the kingdom of Goguryeo pledged allegiance to the Tang court, maintaining friendly relations. The Tang emperor bestowed upon King Geonmu of Goguryeo the titles of Pillar of State, Prince of Liaodong, and King of Goguryeo. Tang Daoist priests then traveled to Goguryeo bearing portraits of the Celestial Worthy, lecturing on the *Laozi* and spreading Han Chinese culture.
During the Zhenguan reign of Emperor Taizong of the Tang Dynasty, Gai Suwen of Goguryeo summoned his tribal leaders under the pretense of a grand military review, setting up a banquet and inviting the ministers to attend. When the ministers arrived, Gai Suwen launched a massacre, killing over a hundred people, then charged into the palace and murdered King Jianwu, throwing his body into a ditch. Gai Suwen installed Jianwu's younger brother, Jang, as king and appointed himself as "Molliji" (equivalent to the Tang Dynasty's Minister of War and Imperial Secretary combined). From then on, he monopolized state affairs, ruling with ruthless cruelty.
When the kingdom of Silla was under attack by Goguryeo and its ally Baekje, who cut off Silla's tribute route to the Tang court, Silla sent an urgent plea for help. Emperor Taizong of Tang dispatched the envoy Xuanzang with an imperial seal to mediate. The Goguryeo general Yeon Gaesomun told Xuanzang, "When the Sui dynasty invaded us, Silla seized five hundred li of our land. Unless they return it, our army will not stop." Xuanzang replied, "Why dwell on old grievances? The Liao region was once Chinese territory, yet the Son of Heaven does not claim it. How can Goguryeo defy his decree?" Yeon Gaesomun refused to listen.
Emperor Taizong of Tang decided to campaign against Goguryeo: "The regent killed his sovereign and slaughtered ministers like trapping beasts in a pit, causing widespread resentment. Wouldn't my campaign against him be justified?"
Emperor Taizong of Tang wanted to personally lead an invasion of Goguryeo. His ministers urged him not to go. Imperial advisor Chu Suiliang warned, "If the campaign fails, you'll have to raise another army; that will anger the soldiers, and with morale shaken, victory becomes uncertain." The emperor agreed, but when another official slandered Chu, he hesitated. Chu then submitted a memorial: "Let me use the body as a metaphor: the capital is the heart, the borders are the limbs, and distant lands are beyond the extremities. The king of Goguryeo was appointed by Your Majesty; his murder by the regent is treason and must be punished. But you need only send one or two brave generals with a hundred thousand elite troops—it's as easy as spitting into your palm. In the past, ordinary men like Hou Junji and Li Jing conquered Gaochang and the Turks. The veteran warriors who fought beside you still have their spirit; just give the order, and they will march."
Emperor Taizong was determined to conquer Liaodong and ignored Chu Suiliang's advice. He said, "I understand the reasoning—abandoning the root for the branch, giving up the high for the low, forsaking the near for the far—all three are unwise, and the campaign against Goguryeo is no exception. Yet Gai Suwen killed his king and terrorized his ministers, and the people there are stretching their necks for rescue—this is Goguryeo's moment of downfall."
Emperor Taizong personally led the six armies forward
Later, the idiom "Reaching Out to Take" came to be used to describe something extremely easy to obtain.
Source: *New Book of Tang*, "Biography of Chu Suiliang"
Meaning of the Idiom: Later, the Chinese idiom "唾手可取" came to describe how something extremely easy to obtain.