Complex sentence: In the early months of 1644, Li Zicheng declared himself the founder of the Shun and marched towards the Ming capital from Shaanxi, roughly following the line of the Great Wall to neutralize its heavily fortified garrisons.
Split into simpler sentences: In the early months of 1644, Li Zicheng declared himself the founder of the Shun and marched towards the Ming capital from Shaanxi. His route roughly followed the line of the Great Wall, in order to neutralize its heavily fortified garrisons.