The late period of Silla was marked by frequent coups, reflecting the internal instability and political volatility within Silla society. These events played a crucial role in shifting the power dynamics and reshaping the political order within Silla. When successful, new monarchs would actively engage in foreign diplomacy, especially strengthening relations with the Tang, as part of their efforts to overcome political instability and secure international legitimacy. Such diplomatic activities were essential for elevating Silla's international standing and establishing the legitimacy of the new monarchy both domestically and internationally. For the kings who ascended to power through coups during the late Silla period, prioritizing relations with Tang, the major power of the time, was a critical strategy in the international political environment. Friendly relations with Tang provided Silla with political support and stability, contributing to overcoming internal instability caused by coups and securing recognition and support from the international community. The dispatch of envoys to Tang by the kings who ascended through coups right after their coronation can be seen as part of this strategy, revealing Silla's intention to emphasize its legitimacy internationally and to secure internal political stability through diplomatic relations. Specifically, the use of unconventional diplomatic strategies by Kings Seondeok and Heondeok, such as intentionally concealing the news of their accession, can be interpreted as an effort to overcome the legitimacy deficit caused by the coups. The prioritization of diplomacy with Tang by the monarchs of late Silla who came to power through coups was a pragmatic choice considering Silla's position in the international political environment. The close diplomatic relations with Tang brought political stability and international support to Silla, playing a significant role in overcoming the internal instability caused by the coups. This strategy indicates Silla's efforts to secure international legitimacy and overcome the political instability resulting from the coups. On the other hand, the lack of official diplomacy with Japan suggests that Silla did not see significant benefits in diplomatic relations with Japan at the time or placed more emphasis on its relations with Tang. This indicates that Silla's foreign policy was focused on securing its position and legitimacy in the international arena, primarily through its relationship with Tang, rather than establishing formal diplomatic ties with Japan.