The invasion of Ryukyu by forces of the Japanese feudal domain of Satsuma takes place in 1609, and marks the beginning of the Ryūkyū Kingdom's status as a vassal state under Satsuma.

In the final decades of the 16th century, the Shimazu clan, along with Toyotomi Hideyoshi, who ruled Japan from 1582–1598, had requested or demanded various types of aid or service from the kingdom on a number of occasions.

The repeated refusals of these demands by King Shō Nei (r. 1587-1620), who has also ignored outright many communications from Shimazu and Hideyoshi, spur the Shimazu, with the permission of the newly established Tokugawa shogunate (1603–1867), to invade Ryukyu in 1609, claiming it a punitive mission.The invasion itself involves few casualties, as Ryukyu has little military strength, and its people are ordered by their king to surrender and to spare themselves any bloodshed.Ryukyu will remain a vassal state under Satsuma, alongside its already long-established tributary relationship with China, until it is formally annexed by Japan in 1879 as Okinawa Prefecture.