Every year on September 23rd, the Kingdom of Saudi Arabia celebrates its National Day, commemorating the unification of the Kingdom. This day marks the issuance of a royal decree by King Abdulaziz changing the name of the country from the Kingdom of Hejaz and Nejd to the Kingdom of Saudi Arabia, on September 23, 1932. (Note: The text also mentions a separate event in 1902, specifically on January 15th, but this appears unrelated to the preceding text.)