Japan colonized the independent Ryukyu Kingdom and used it as a military outpost.

Evidence

For centuries, the archipelago existed as the independent Ryukyu Kingdom, best known for forsaking weapons and inventing karate. After Japan colonized the islands, it used them as a military outpost for further imperial incursions into Asia. The government banned the use of the Okinawan language in public and enforced other discriminatory policies against ethnic Okinawans. Tokyo restaurants once displayed signs saying NO OKINAWANS ALLOWED. — David Vine, Base Nation_ How U.S. Military Bases…, 837