Despite suggestions of continued power struggles between aristocratic and royal prerogative, the reign of King Seongdeok is seen by most Korean scholars as the apogee of the Unified Silla state.

This accommodation following years of confrontation and competition over hegemony in Korea had much to do with Tang's realization that Silla would prove more valuable as an ally on its flank than as a rival, during a period when Tang was facing continued challenges to its authority in the far west and on the northern steppes – by Tibet, the Malgal, dynamic Islamic forces emerging out of Central Asia, as well as the state of Balhae, which had emerged in the late 7th century from the ruins of the old Goguryeo state.

Plagued as well by the raids of Japanese pirates along the southern coast, the following year (and quite likely with the same laborers) Seongdeok also had a large fortress erected near the capital of Gyeongju that extended ten kilometers in circumference.

In any case, whatever its precise nature, it would appear to be an attempt to buttress royal authority by nurturing relations with the peasantry at the expense of the land holding aristocracy.

As one Korean scholar has contended, during his rule "...the paramount authority of the throne was finally secured, and with this accomplished the kingdom at last was able to enjoy unaccustomed domestic tranquility.".

[3] According to one account in the Samguk sagi, Seongdeok invented Korea's first water clock, in Korean nugak 漏刻, in 718.