It was united in 935 and it was united by the silla kingdom.
Silla in 676 CE.
During the time of the near fall of Tang dynasty in China, WANG KIEN ruled the revolution in Korea and colonized the kingdom of Paekche and Silla.
The Three Kingdoms of Korea (Goguryeo, Baekje and Silla) existed from 57 AD until Silla's triumph over Goguryeo in 668. This marked the transition to the North and South States period of Unified Silla in the South and Balhae in the North.
After the Silla kingdom collapsed, the Goryeo kingdom emerged as a dominant power in the Korean peninsula. Goryeo ruled from 918 to 1392 and was known for its advancements in arts, culture, and technology.
The three kingdoms in Korea were named Goguryeo, Baekje, and Silla.
Silla did, way back then in the 3 kingdoms period
The crowns of Silla were made in the Korean kingdom of Silla approximately in the fifth and sixth centuries of the Common Era. Of the ten fully golden crowns in the world, eight are from the Korean Peninsula. Out of these, six are from Silla, and two are from the neighboring Gaya confederacy.[1] These crowns were excavated in Gyeongju, the former capital of Silla, and are designated National treasures of South Korea. The Silla crowns are very fragile and weigh more than one kilogram. The Silla kings probably did not wear the golden crowns like hats. They were probably used only for formal and ceremonial occasions. Some scholars believe that the crowns were never worn at all but made specifically as burial goods.
One of the main kingdoms of Korea that did not develop after colonization by the Chinese Han was the Unified Silla kingdom. The other three main kingdoms that emerged during this period were Goguryeo, Baekje, and Gaya.
Korean society has been strongly influenced by Confucianism, Buddhism, and traditional Korean shamanism. These influences have shaped social norms, values, and cultural practices in Korea.
Confucianism and Buddhism
Though the founding date is debated by historians, the recorded history of Korea began under the kingdom of Gojoseon. Gojoseon suffered defeat by the Han dynasty of China, and became divided into many different states. After a series of conquest and wars, the Three Kingdoms of Korea emerged (Goguryeo, Baekje, and Silla). Though Goguryeo emerged successful in several wars with the Chinese, Silla (allied with the Tang of China) conquered Baekje and Goguryeo and divided Goguryeo's territory with Tang China. Silla's unification of Korea was short-lived and was soon replaced with the kingdom of Goryeo. Despite being small in size, Goryeo managed to repel the invading Liao kingdom and the Jurchen Jin dynasty but was defeated by the Mongols. Though not conquered, the kings of Goryeo from then on were puppets of the Mongols. It was because of this fact that Goryeo was overthrown and replaced by the kingdom of Joseon. Joseon, unlike its predecessors was not warlike and instead embraced art and literature. Despite this Joseon still managed to soundly defeat the invading Japanese in 1592-1598. However, Joseon shunned Western ideas and technologies, a stance that led to Japanese annexation. After Korea's liberation from Japan, the Communist North invaded the South resulting in the Korean War. As a result of this war, Korea became divided into the Democratic People's Republic of Korea (North Korea) and the Republic of Korea (South Korea).