According to archaeological evidence in the third and fourth centuries some of the city-states of Byeonhan evolved into the Gaya confederacy, which was later annexed by Silla, one of the Three Kingdoms of Korea.

[3] Although most commonly referred to as Gaya (가야; 加耶; 伽耶l; 伽倻; [kaja]), probably due to the imprecision of transcribing Korean words into hanja, historical sources use a variety of names, including Garak (가락; 駕洛; 迦落; [kaɾak]), Gara (가라; 加羅; 伽羅; 迦羅; 柯羅; [kaɾa]), Garyang (가량; 加良; [kaɾjaŋ]), and Guya (구야; 狗耶; [kuja]).

[4] According to Christopher I. Beckwith, "The spelling Kaya is the modern Korean reading of the characters used to write the name; the pronunciation /kara/ (transcriptionally *kala) is certain.

It is thought that the meaning of "Korea" was initially preserved in Japanese in the word "Kara" which later expanded to include "China, then mainland East Asia" and, more recently, an even more vague sense of "the nations overseas or foreign countries".

[6] Linguists, including Vovin and Janhunen, suggest that Japonic languages were spoken in large parts of the southern Korean Peninsula.

[9] According to a legend written in the Samguk yusa in the 13th century, six eggs descended from heaven in the year AD 42 with a message that they would be kings.

Based on archaeological sources and the limited written records, scholars have identified the late 3rd century as a period of transition from Byeonhan to Gaya, noting increasing military activity and changing funerary customs.

This transition was also associated with the replacement of the previous elite in some principalities (including Daegaya) by elements from the Buyeo kingdom, which brought a more militaristic ideology and style of rule.

Traditionally, the Gaya Confederacy enjoyed good relations with Japan and Baekje, such as when the three states allied against Goguryeo and Silla in the Goguryeo-Wa War.

After a period of decline, the confederacy was revived around the turn of the 5th and 6th centuries, this time centered on Daegaya of modern Goryeong.

[21] One such example was the Sillan General Kim Yu-sin who played a critical role in the unification of the Three Kingdoms of Korea.

[23][24] Archaeological evidence suggests that Gaya polities were the main exporter of technology and culture to Kyushu at that time.