Unified Silla is the name often applied to the Korean kingdom of Silla after 668.
During the first few centuries of the first millennium of the Common Era, the Korean Peninsula was divided up between three warring kingdoms, Silla, Baekje and Goguryeo. This era of Korean history is known as the Three Kingdoms period.
In 660, King Munmu of Silla ordered his armies to attack Baekje. General Kim Yu-shin, aided by Tang forces, defeated General Ge-Baek and conquered Baekje. In 661, he moved on Goguryeo but was repelled. King Munmu ordered General Kim to launch another campaign in 667 and, in 668, Goguryeo fell. King Munmu was the first ruler ever to look upon the Korean Peninsula as a single entity. As such, the post-668 Silla kingdom is often referred to as Unified Silla.
Unified Silla lasted for 267 years until, under King Gyeongsun , it fell to Goryeo in 935.
The name "Unified Silla" is a term that likely dates from after the division of Korea in 1945, and to some degree likely reflects modern-day political longings. Because of this, some historians suggest the term "South and North States " to include Balhae.