The Second Manchu Invasion refers to the military campaign by the Manchu people in the early 17th century, specifically from 1644 to 1645. This invasion aimed to overthrow the declining Ming Dynasty in China. The Manchus, who were originally from the region now known as Northeast China, took advantage of internal strife within the Ming to launch their attack. The invasion culminated in the fall of Beijing in 1644, leading to the establishment of the Qing Dynasty. This marked a significant shift in Chinese history, as the Qing would go on to rule for nearly three centuries, expanding China's territory and influence across Asia.