2) Social Change
Iron culture brought important changes to bear on all aspects of ancient society. The traditional clan societies collapsed through a string of wars, conquests, incorporations, and submissions. Emerging out of the chaotic transition of society was the dominant ruling class based on consanguinity ties. Even the ruling class was graded into various levels of hierarchical order. The king's authority depended very much on the whimsical changes of the ruling class. In BUYEO and GOGURYEO, the king was elected out of the ruling members but the elected king was constrained in exercising his authority. In BUYEO, the king, blamed for a long drought, was replaced or met his death in the hands of contending members of the ruling class. In the early period of GOGURYEO, the SUSANG of the bureaucracy called "Daetaero" was an elective position subject to replacement. He was forced to abandon his position, when he committed a serious misbehavior which adversely affected the state affairs.
With the passage of time, however, the king stabilized his power, as the hereditary system was firmly established. The incorporation of new territories established tributary relations of hierarchical order between the conqueror and the conquered. Together with this, the governing of the enlarged territories made it imperative to strengthen the power base of the king. King Euryo of BUYEO managed to govern the state from the age of six by virtue of the king,s authority put on the bedrock of hereditary system. Succession to the king no longer went from brother to brother but from the father to the son. King Sonoburo of GOGURYEO was the first to hand his power to his son, defying the earlier practice of surrendering it to a sibling of the same blood.
Despite the centralization of the ruling power, the king's authority of the tribal leagues was no match for the absolute power exercised by the kings of the three kingdoms. The ruling power of the tribal leagues rested not so much with the king himself as the royal family or the queen's family. Often, tribal chiefs had strong influence to be reckoned with in changing the king. They lived a luxious life with the fortunes amassed from NOBI. As the king gathered his strength, they formed a new force in the central government and made their aristocratic status hereditary.
3) Religion
Religious rituals were not divorced from politics. DANGUNWANGGEOM was both the ruler and the master of religious rituals. However, the centralization of the king's authority which paralleled territorial expansion did much to separate politics from religious rituals. Rulers came to be content with their political role, while ritual masters were presiding over religious rituals.
In SAMHAN, the ritual master was called "CHEONGUN," literally heavenly man. He was positioned to preside over sanctuary called "SODO" where ritual service was performed under a tree decorated with bells and drums. SODO offered the place for criminals to hide: Once they were in, they were able to escaped arrest. In the primitive form of MUDANG, the ritual master claimed himself to the capability of moving deities in his favor. However, he changed the perception of himself from the omnipotent master to a mediator who solicited deity's good will. Of all religious rituals, the festive ritual after the Autumn harvest was most important and impressive. It was the equivalent of the Thanks-giving festival celebrating good harvest for the year and praying for more to come. The festivals of this nature were the common denominator of all tribal leagues but each was given a different name: It is called "YEONGGO" in BUYEO, "Dong Mang" in GOGURYEO, "MUCHEON" in Tong Ye, and the October festival in SAMHAN. No less important was the festival JESA to heaven after the season of sowing. Such a festival brought all people together across the state and entertained them with food and drink. The nationwide festival served as the social glue for different ethnic groups and classes, but the clan-centered collectivity remained diehard
Noteworthy along this line was the popular belief in the immortality of soul, which inspired people to lavish funeral rituals. The idea behind such a funeral practice was the reasoning along "if soul is immortal, there must be a netherland one goes after death." In BUYEO, funeral took place five months after death. They froze the corpse to keep it from be decayed. Personal belongings were buried with the deceased person. There was even the practice of burying an old or invalid person alive. The same can be said of the funeral of GOGURYEO. Tomb was a kind of earthen mound made up of stones piled up in a pyramid shape. The practice of delaying burial was widely spread in SAMHAN and the animals used in the funeral ritual were cows and horses.

Imitated wings of a big bird were used in a symbolic gesture to give wings to the soul so that it flies into heaven: A big bird of any kind symbolized a bridge linking this world to the heavenly world.
The funeral was linked to ancestor worship. Ancestor worship is the extension of filial piety to parents beyond their life time and this concept was further intensified by emphasis on the patriarchal family which emphasized the hereditary relation between father and son. Ancestor worship believes in the timelessness of the family lineage which goes back to a time immemorial and stetches out into the infinite future. Respect for the deceased ancestors led to worship for the national founder and ritual service for him became an annual event of national scale.
JEOMBOK was widely practiced. BUYEO saw a ritual service performed to JESA for the heavenly protection of its armed forces before they went to battlefield. In this ritual, a cow was killed as a sacrificed offer to the deity. From the shape of a dead cow, it was possible to divine the fate of a
state in crisis. If its toes were found split, it heralded a misfortune to come upon. If the toes were put together, something auspicious was predicted to come along. According to SAMGUKSAGI (The Annal of Three Kingdoms), prognosis was made of the fate of a baby still in the womb, that is, whether he would become a king. Resort to JUMSOK' prognosis regarding the fate of a family or an individual was widely practiced in the ruling class and commoners.