1. Missouri became a state: August 15, 1821, marked an important day in Missouri history as it was the day the state was officially granted statehood. After being part of the Louisiana Territory and then the Missouri Territory, it became the 24th state in the United States.

2. The original state capital: St. Charles served as Missouri's first capital from August 15, 1821, until November 1826 when the capital was moved to Jefferson City. St. Charles was chosen because of its central location and easy access to the Missouri River.

3. Major Civil War battle: On August 15, 1863, the Battle of Lone Jack took place in Jackson County. It was one of the largest Civil War battles to take place in Missouri, and although the Confederate forces won, they suffered significant casualties. Today, a museum in Lone Jack commemorates the event.

4. The first streetcar line: St. Louis became the first city in the world to have a successful streetcar line on August 15, 1877. The line ran from Union Depot to Carondelet, and the service was very popular among residents. The streetcar era in St. Louis lasted until the 1960s when cars and buses took over.

5. Missouri State Fair: The Missouri State Fair, one of the state's largest annual events, typically takes place around August 15th. Started in 1901, the fair includes a wide range of activities and attractions, such as carnival rides, live entertainment, agricultural exhibits, and competitions. The state fairgrounds are located in Sedalia, Missouri.