Which state celebrated its fiftieth anniversary in 2009 and was once an independent kingdom?

The state that celebrated its fiftieth anniversary in 2009 and was once an independent kingdom is Hawaii. Hawaii became a state of the United States on August 21, 1959, which means that 2009 marked fifty years since that event. Prior to its annexation, Hawaii was a sovereign nation, known as the Kingdom of Hawaii, with its own royal family and government. This unique historical background distinguishes Hawaii from the other options listed.

Alaska, while significant in its own right, does not have a history as an independent kingdom; it was purchased from Russia and became a state in 1959 as well, but it did not celebrate a fiftieth anniversary in 2009. Puerto Rico is a territory, not a state, and has a different status regarding its relationship with the United States. Oregon, although a state, does not have an independent kingdom history and became a state much earlier, in 1859. Therefore, Hawaii stands out as the correct answer due to its distinct combination of statehood anniversary and historical status as a former kingdom.