The Yan State in the north of Qi State was relatively weak and was often invaded by the neighboring Shanrong tribes. The Shanrong tribe made a living by hunting and did not engage in agricultural production. When they were short of food, they went to Yan State to plunder.
In 664 BC, Shan Rong soldiers and horses launched a large-scale attack on Yan State, and Yan asked Qi State for help. At that time, when Qi Huanzheng, the king of Qi, was establishing his hegemony, he took it as his own duty to defend the Central Plains and get rid of the barbarians and Di. He personally led the army to drive out the Shanrong.
When Shanrong heard that Qi’s army was coming to kill them, they immediately fled from Yan. Duke Huan of Qi adopted the advice of Prime Minister Guan Zhong and led his army to pursue the Shanrong northward until they reached the Guzhu Kingdom (now Jinxi County, Hebei). Milu, the king of Shanrong, fled to the Guzhu Kingdom. Duke Huan of Qi led his army to attack the Guzhu Kingdom, but was deceived into the vast desert by Guzhu's general Huang Hua. The Qi army walked in the desert for a day and a night, completely lost their way. Fortunately, Guan Zhong thought that old horses could recognize old roads, so he immediately found some old horses in the army. Under the leadership of several old horses, the army finally walked out of the desert. After the Qi army came out of the desert, they quickly defeated the Guzhu army and eliminated the remaining Shanrong forces.
As for Duke Huan of Qi’s practice of ceding land to the State of Yan, I think that in order to prevent Lord Yan from violating etiquette and law, Duke Huan of Qi ceded his own land to the State of Yan. But Duke Huan of Qi has no right to dispose of the land of Qi State privately. It can be seen that Duke Huan of Qi's approach seems to be "respecting etiquette and respecting the king", but in fact it is reckless. The root cause of Duke Huan of Qi's self-contradictory approach was that he did not take the Emperor of Zhou seriously, nor did he pay attention to the so-called "etiquette". His so-called respect for the king and courtesy is just a gimmick for show. Of course, the reason why Duke Huan of Qi dared to do this was because the Zhou royal family was too weak, and they could do whatever they wanted.
Then again, if you're not strong enough, it's good if people can respect you on face, but do you really expect them to respect you deep down? Later, during the Warring States Period, even this kind of respect for face was gone. At that time, the Zhou royal family was truly miserable!