The ascension of Sun Quan to the throne as the Emperor of Wu in 229 CE officially established the state of Eastern Wu and solidified the tripartite division of China, alongside the states of Shu Han under Liu Bei (and later his successors) and Wei under Cao Pi.

Sun Quan's rise to power was a culmination of years of political maneuvering and military campaigns that began under the leadership of his elder brother, Sun Ce, and then his father, Sun Jian, both of whom were instrumental in establishing the Sun family's power base in the Jiangdong region. After Sun Ce's untimely death, Sun Quan took over the reins of power and continued to expand and consolidate his control over the southeastern territories of China, which included key areas along the Yangtze River and the coastal regions.

The decision to declare himself emperor came after Sun Quan had firmly established his authority in the region and in the wake of the political shifts following the establishment of Cao Wei and Shu Han. By proclaiming himself Emperor of Wu, Sun Quan not only asserted his independence from the other states but also legitimized his rule over his territories, providing a strong counterpoint to the claims of Cao Pi and Liu Bei.

Sun Quan's reign as Emperor of Wu was characterized by both military and administrative achievements. Militarily, he is perhaps best known for his role in the Battle of Red Cliffs in 208 CE, where, allied with Liu Bei, he successfully repelled Cao Cao's massive invasion force. This battle was a turning point in the Three Kingdoms period and played a crucial role in preventing Cao Cao from dominating all of China.

Administratively, Sun Quan was known for his effective governance. He implemented reforms to improve agricultural productivity, strengthen the navy, and encourage trade and commerce, particularly maritime trade. These policies not only boosted Wu's economy but also helped in maintaining the loyalty and support of his subjects.

Sun Quan's rule also saw diplomatic efforts and alliances, most notably with the state of Shu Han, though these alliances were often marked by mutual suspicion and shifting loyalties. Despite occasional conflicts and confrontations with Wei and Shu, Wu under Sun Quan maintained a strong defensive position, safeguarding its territories from major invasions.

The establishment of Wu as an independent state under Sun Quan was a key factor in the prolonged stalemate that characterized the Three Kingdoms period. It represented the fragmentation of the Han Empire into three distinct and powerful states, each with its unique strengths and weaknesses.