Why does Liang have to go north? Personally, I think there are three reasons,
The first is to inherit Liu Bei's legacy and repay Liu Bei's kindness and trust. Liu Beisan Gu Maolu invited Zhuge Liang out and reused it, and when he was entrusted to the White Emperor's city, he entrusted him with important state affairs, and he had absolute trust in Zhuge Liang.
The second is external reasons, after Guan Yu carelessly lost Jingzhou, Liu Bei launched the Battle of Yiling, was defeated by Lu Xun, it can be said that this time is the internal and external difficulties, after the loss of Jingzhou, the goal set by the "Longzhong Pair" was broken, and a new breakthrough must be found, at this time the State of Wei occupied nine states, the State of Wu also occupied three states, only Shu Han was a state, the weakest one, plus the fiasco of the Battle of Yiling, if it developed peacefully, how to catch up, it could not surpass Wei, Wu, just like we snowball, a small snowball no matter how fast it rolls, It is also better than a big snowball rolling around, so Zhuge Liang's Northern Expedition caused some pressure on the Wei state, not only to prevent Wu, but also to prevent Shu, the life and production of the Wei state were interfered with, and the Northern Expedition also caused a certain amount of internal strife within the Wei state, and rebellions occurred in many places.
The third is internal reasons, Liu Bei's founding base is to restore the Han room, to the Han room orthodoxy, if Zhuge Liang did not go north, Shu Han lost its legitimacy, and Cao Wei usurped Han, Liu Zhang lived alone in a corner, there is no difference.
Secondly, after Liu Bei's death, there were rebellions in many places, and there were many factions within the Shu Han Dynasty, one of which was a small ninety-nine, and the Northern Expedition just shifted everyone's contradictions, making the internal unity external, unprecedented unity, and stronger cohesion.
Because of the above three reasons, so Zhuge Liang a total of five times the Northern Expedition, if the first Northern Expedition is not because of the loss of the street pavilion, the Northern Expedition is not likely to succeed aside, but Liangzhou is a stable income bag, although Zhuge Liang's Northern Expedition was not successful, but also did it bow down, and died.
Welcome to like friends like point attention Oh! Thank you!