Sima Yi won. Well technically, it was his grandson Sima Yan who ended the Three Kingdoms and reunited China.

Sima Yi was an adviser under Cao Cao who rose through the ranks of the Wei. He was very close to Cao Cao's successor Cao Pi and was also trusted by Cao Pi's successor Cao Rui. Cao Rui eventually feared that Sima Yi was too powerful and so on his deathbed entrusted his son Cao Fang to his uncle Cao Shuang. However, Sima Yi led a coup which overthrew Cao Shuang and came to dominate the Wei court. Sima Yi was succeeded by his son Sima Shi, who in 254 deposed Cao Fang when the latter tried to overthrow him and replaced him with someone else. In 263, Sima Shi led the Wei in defeating and absorbing Shu. When Sima Shi died, he passed power to his brother Sima Zhao. Sima Zhao's son Sima Yan deposed the last Wei emperor in 265 and established the Jin, going on to destroy the Wu in 279.

Cao Cao basically set up the base for reunification which Sima Yi took advantage of.

Edit 1: Added details.

Edit 2: Spelling.

Hiya!

Could you please clarify your question? Are you asking about a particular state/faction/cultural group establishing dominance during the Three Kingdom Period?

Thanks!