(668 CE - 935 CE): Unified Shilla

통일 신라 - The Unified Shilla Period

The curtain finally fell upon the long-running drama of the Samguk Sidae when the Shilla kingdom defeated its rivals and gained control over the majority of the Korean peninsula by 668 CE. After the forces of Shilla crushed the Baekje kingdom in 660, the Shilla kingdom and its ally, the mighty Tang Empire, assaulted the Goguryeo kingdom. Under the reign of King Munmu 문무왕, Goguryeo fell to the allied Shilla-Tang forces. Despite the tenacity of the Goguryeo kingdom, its own internal divisions within the court severely weakened it politically and militarily and it was no longer able to hold off the combined attacks of its powerful foes. 

Immediately after the conquest of the Baekje and Goguryeo kingdoms, Shilla's dubious ally had its own designs for the Korean peninsula. The Tang Empire demanded that Shilla submit itself and become a vassal state, a demand that Shilla rejected. King Munmu organized an effort to drive out the would-be Tang occupiers and establish Korean control over the peninsula. In 676 CE, after years of fierce confrontation, the Tang Empire's armies were effectively driven out and Shilla remained a strong and cohesive independent kingdom.

Thus began a period that modern people refer to as "통일 신라," the "Unified Shilla" Period.

Sources:

http://people.cohums.ohio-state.edu/bender4/eall131/EAHReadings/module02/m02korean.html

Seth, Michael J. A Concise History of Korea. Rowman & Littlefield Publishers, Inc. 2006