The Great Wall of China is a collection of walls built by different dynasties over a millennium.
1. The wall is a collection of walls built by different dynasties over a millennium. Over the years the shifting borders extended beyond certain sections that were once part of the wall. The wall that is known as the “actual” great wall was constructed and connected by the Ming Dynasty, which connected parts of an existing wall as well as building new sections to create an incredible 6259km long wall.
2. The wall wasn’t for defense- at least not the entire wall. I’m not sure how anyone can conclude that a wall alone can feasibly stop an invasion that will probably number in the tens or hundreds of thousands. Also, you can’t see the wall from space just like how you can’t see a normal road from space.
It was for border control to stop migration, an early warning system, as well as a rapid transportation and communication system. At 5–6.5 meters wide, it couldn’t stop a full-scale invasion, but it’s the width of a road allowing rapid troop reinforcements. The primary military function was centered on the many fortresses it connected.
3. The Mongols didn’t just “go around” the Great Wall. The wall wasn’t at it’s the fullest extent at the time of the invasion, and they had to employ a whole number of other strategies to breach it including bribing the army that actually guarded a section of it. Also at the time, there were 3 competing powers in China, not one unified dynasty.
The 6000km+ great wall that is known today was completed after the Mongol yuan dynasty was kicked out of China. The eventual Qing dynasty successors also originated from Manchuria outside of the wall, but they didn’t breach it, the General that guarded it (who also commanded the largest army in that region) opened the gates. He did this when he was surrounded by 2 armies, the Manchurian forces outside of the wall and a peasant rebellion inside the wall. The capital was sacked and the General’s entire family was slaughtered by the latter, so he sided with the Manchurians. You can see that both times, a pivotal factor was subversion and not brute force.
4. The Wall was redundant for much of its existence. Firstly the Ming dynasty only built the wall we know today after the Mongols were greatly weakened. But construction continued until the end of the Ming, and during the Qing dynasty (which lasted ~300 years) most of the northern areas were conquered which made the majority of the wall within the border.