1. On June 21, 1779, the Battle of Kealakekua Bay took place. This was a significant event in Hawaiian history as it resulted in the death of Captain James Cook, a British explorer who is credited with introducing the Hawaiian Islands to the Western world.

2. In 1834, on June 21, the Kingdom of Hawaii established its first official post office. This was a crucial development in the island nation's infrastructure and allowed for easier communication and trade with the rest of the world.

3. On June 21, 1847, King Kamehameha III declared a national holiday to honor the Hawaiian people's ancestors known as 'Kamehameha Day.' This unique Hawaiian holiday is still celebrated today as a recognition of the legacy of King Kamehameha.

4. In 1893, on June 21, the last monarch of Hawaii, Queen Liliuokalani, was forced to surrender her throne to the United States government. This event marked the end of Hawaii's independence and led to Hawaii being annexed as a US territory.

5. June 21, 1969, marked the opening of the Ala Moana Center, one of the largest shopping malls in the world at the time. This center helped to solidify Hawaii's status as a major tourist destination and helped to drive the state's economy.