Neo-Confucianism, also known as the "New Confucianism," emerged in China during the Song Dynasty (960-1279 CE) as a response to the growing popularity of Buddhism and Taoism. It was a synthesis of Confucian, Taoist, and Buddhist ideas, creating a new philosophical and ethical system that would greatly influence not only Chinese culture but also other cultures throughout East Asia.

One of the main reasons for the spread of Neo-Confucianism was its emphasis on moral cultivation and the pursuit of inner harmony. Confucianism had always placed a strong emphasis on moral values and social order, but Neo-Confucianism took it a step further by incorporating Taoist and Buddhist teachings on meditation and spiritual enlightenment. This appealed to many people who were seeking a more spiritual and introspective approach to life, especially during a time when China was facing political instability and social upheaval.

The spread of Neo-Confucianism was also facilitated by the support of the ruling class. The Song Dynasty government actively promoted Neo-Confucianism as the official state ideology, and many government officials and scholars were trained in Neo-Confucian thought. As a result, Neo-Confucianism became deeply ingrained in Chinese society, influencing everything from education to government policies.

The influence of Neo-Confucianism also spread through trade and cultural exchange. As China's influence expanded through trade, so did its cultural and philosophical ideas. Neo-Confucianism was introduced to Korea, Japan, and Vietnam through trade and cultural exchange, where it was embraced and adapted to fit the local cultures. In Korea, Neo-Confucianism became the dominant ideology and had a significant impact on the country's social and political structures. In Japan, Neo-Confucianism was adopted by the samurai class and played a crucial role in shaping their code of ethics and behavior.

Furthermore, Neo-Confucianism's emphasis on moral cultivation and social harmony also appealed to other cultures outside of East Asia. In the 19th and 20th centuries, Neo-Confucianism spread to the West, where it was studied and adapted by Western scholars and philosophers. Its ideas of moral cultivation, social responsibility, and the pursuit of inner harmony resonated with Western thinkers, and it has had a lasting influence on Western philosophy and ethics.

In conclusion, Neo-Confucianism spread through various means, including government support, trade, and cultural exchange. Its emphasis on moral cultivation and inner harmony appealed to people from different cultures, and it greatly influenced not only East Asian societies but also other cultures around the world. Today, Neo-Confucianism continues to be a significant philosophical and ethical system, with its ideas still relevant and influential in modern society.