The earliest known Korean pottery dates back to around 8000 BCE or before, and evidence of Mesolithic Pit-Comb Ware culture or Yungimun Pottery is found throughout the peninsula.

An example of a Yungimun-era site is in Jeju-do.

Jeulmun or Comb-pattern Pottery is found after 7000 BCE, and pottery with comb-patterns over the whole vessel is found concentrated at sites in west-central Korea when a number of settlements such as Amsa-dong exist.

Jeulmun pottery bears basic design and form similarities to that of the Russian Maritime Province, Mongolia, and the Amur and Sungari River basins of Manchuria and the Jomon culture in Japan.

Examples of Early Jeulmun settlements include Seopohang, Amsa-dong, and Osan-ri.

Deep-sea fishing, hunting, and small semi-permanent settlements with pit-houses characterize the Early Jeulmun period (from about 6000 BCE to about 3500 BCE).

Radiocarbon evidence from coastal shell midden sites such as Ulsan Sejuk-ri, Dongsam-dong, and Ga-do Island indicates that shellfish were exploited, but many archaeologists maintain that shellmiddens (or shellmound sites) did not appear until the latter Early Jeulmun.

At least fourteen sites from Korea's Middle Jeulmun period (circa 3500-2000 BCE) have yielded evidence of cultivation in the form of carbonized plant remains and agricultural stone tools. (Choe, C P and Martin T Bale (2002) Current Perspectives on Settlement, Subsistence, and Cultivation in Prehistoric Korea. For example, Crawford and Lee, using AMS dating techniques, directly dated a domesticated foxtail millet (Setaria italica ssp. italica) seed from the Dongsam-dong Shellmidden site to the Middle Jeulmun (Crawford, Gary W. and Gyoung-Ah Lee 2003. Agricultural Origins in the Korean Peninsula. Antiquity 77(295):87-95.).

Another example of Middle Jeulmun cultivation is found at Jitam-ri (Chitam-ni) in North Korea.

A pit-house at Jitam-ri yielded several hundred grams of some carbonized cultigen that North Korean archaeologists state is millet.

However, not all archaeologists accept the grains as domesticated millet because it was gathered out of context in an unsystematic way, only black-and-white photos of the find exist, and the original description is in Korean only.

Cultivation was likely a supplement to a subsistence regime that continued to heavily emphasize deep-sea fishing, shellfish gathering, and hunting.

"Classic Jeulmun" or Bitsalmunui pottery in which comb-patterning, cord-wrapping, and other decorations extend across the entire outer surface of the vessel, appeared at the end of the Early Jeulmun and is found in West-central and South-coastal Korea in the Middle Jeulmun.

The establishment of the Korean kingdom of Baekje in 18 BCE heralds the beginning of the Three Kingdoms period.

According to the Samguk Sagi, the founder of Baekje is Onjo, the third son of Goguryeo's founder Jumong and So Seo-no, who leads a group of people from Goguryeo south to the Han River basin.

According to the Chinese record San Guo Zhi, during the Samhan period, one of the chiefdoms of the Mahan confederacy was called Baekje.

According to the detailed account in the Samguk Sagi, Jumong had left his son Yuri in Buyeo when he left that kingdom to establish the new kingdom of Goguryeo.

Becoming King Dongmyeongseong, Jumong had two more sons with So Seo-no, Onjo and Biryu.

When Yuri later arrived in Goguryeo, Jumong promptly made him the crown prince.

Realizing Yuri would become the next king, So Seo-no left Goguryeo, taking her two sons Biryu and Onjo south to found their own kingdoms with their people, along with ten vassals.

She is remembered as a key figure in the founding of both Goguryeo and Baekje.

Onjo settles in Wiryeseong (present-day Hanam), and calls his country Sipje (meaning "Ten Vassals"), while Biryu settleds in Michuhol (present-day Incheon), against the vassals' advice.

The salty water and marshes in Michuhol make settlement difficult, while the people of Wiryeseong live prosperously.

Biryu then goes to his brother Onjo, asking for the throne of Sipje.

When Onjo refuses, Biryu declares war, but loses.

In shame, Biryu commits suicide, and his people move to Wiryeseong, where King Onjo welcomes them and renames his country Baekje ("Hundred Vassals”).

Under pressure from other Mahan states, King Onjo moves the capital from the south to the north of the Han river, and then south again, probably all within present Seoul.

Jinhan is situated in the middle part of the southern peninsula, Mahan in the southwest, and Byeonhan in the southeast.

The state of Baekje, which will soon come to exercise great influence on Korean history, emerges first in the Mahan area; it is not certain when this happened, but Baekje certainly exists by CE 246 because Lelang mounts a large attack on it in this year.

That Baekche is a centralized, aristocratic state melding Chinese and indigenous influence is not in doubt, nor is its growing power: within a century, Baekje has demolished Mahan and continues expanding northward into what today is the core area of Korea, around Seoul.

It is thought that the Korean custom of father-to-son royal succession began with King Kun Ch'ogo (reigned ca. 346-75) of Baekje.

His grandson inaugurates another long tradition by adopting Buddhism as the state religion in 384.

Peninsular geography shapes the political space of Baekje and Goguryeo, and a third kingdom, Silla.

In the central part of Korea, the main mountain range, the T'aebaek, runs north to south along the edge of the Sea of Japan (or, as Koreans prefer, the East Sea).

Approximately three-quarters of the way down the peninsula, however, roughly at the thirty-seventh parallel, the mountain range veers to the southwest, dividing the peninsula almost in the middle. This southwest extension, the Sobaek Range, shields peoples to the east of it from the Chinese-occupied portion of the peninsula but places no serious barrier in the way of expansion into or out of the southwestern portion of the peninsula.

This is Baekje's historical territory.

Two other powerful states had meanwhile emerged north of the peninsula around the time of Christ—Buyeo in the Sungari River Basin in Manchuria, and Goguryeo, Buyeo's frequent enemy to its south, near the Yalu River.

Goguryeo, which also exercises a lasting influence on Korean history, develops in confrontation with the Chinese.

Puyo is weaker and seeks alliances with China to counter Goguryeo but eventually succumbs around 312.

Goguryeo is expanding in all directions, in particular toward the Liao River in the west and toward the Taedong River in the south.

In 313 Goguryeo occupies the territory of Lelang and comes into conflict with Baekje.

The Korean polity of Baekje becomes a full-fledged kingdom during the reign of King Goi (234–286), as it continues its consolidation of the Mahan confederacy, a loose confederacy of chiefdoms that existed from around the first century BCE to the third century CE in the southern Korean peninsula in the Chungcheong Province.

Arising out of the confluence of Gojoseon migration and the Jin federation, Mahan was one of the Samhan (or "Three Hans") confederacies, along with Byeonhan and Jinhan.

Baekje had begun as a member statelet.

In 249, according to the Japanese chronicle Nihonshoki, Baekje's expansion reaches the Gaya confederacy to its east, around the Nakdong River valley.

Chinese records first describe the Korean polity of Baekje as a kingdom in 345.

Geunchogo, the second son of Biryu, the eleventh king of Baekje, had become king in 346 upon the death of the twelfth king, Gye.

His reign seems to have marked the permanent ascendancy of the descendants of the fifth king Chogo (reflected in Geunchogo's name) over those of the eighth king, Goi, and ended the alternating kingship of the two lines.

Having set set out to solidify the royal power within the Baekje state upon ascending the throne, he has reduced the power of the aristocracy and set up a system of local government with regional heads appointed by the court.

He has married a wife from the Jin clan, setting a precedent for his successors, and he has moved the capital to Hansan, today's southeast Seoul.

The first Korean envoy to Japan, an emissary of the government of Baekje, reportedly arrives in 366.

In this year, Geunchogo allies with Silla, which borders Baekje on the east, maintaining a rough balance of power among the Three Kingdoms.

Baekje reaches its greatest geographic extent and political power under Geunchogo, expanding Baekje's territory to the north through war against Goguryeo, while annexing the remaining Mahan societies in the south in 369, completing Baekje's control over all of present-day Jeolla-do.

Gaya confederacy states west of the Nakdong River were also made Baekje dependencies.

During Geunchogo's reign, the territories of Baekje include most of the western Korean Peninsula (except the two Pyeongan provinces).

Baekje is invaded by Goguryeo in 369, but counterattacks in force at the battle of Chiyang.