Please answer a question about the following article about Alaska:

Another Alaskan transportation method is the dogsled. In modern times (that is, any time after the mid-late 1920s), dog mushing is more of a sport than a true means of transportation. Various races are held around the state, but the best known is the Iditarod Trail Sled Dog Race, a 1,150-mile (1,850 km) trail from Anchorage to Nome (although the distance varies from year to year, the official distance is set at 1,049 miles or 1,688 km). The race commemorates the famous 1925 serum run to Nome in which mushers and dogs like Togo and Balto took much-needed medicine to the diphtheria-stricken community of Nome when all other means of transportation had failed. Mushers from all over the world come to Anchorage each March to compete for cash, prizes, and prestige. The "Serum Run" is another sled dog race that more accurately follows the route of the famous 1925 relay, leaving from the community of Nenana (southwest of Fairbanks) to Nome.

What does the Iditarod Trail Sled Dog Race commemorate in Alaskan history?
the famous 1925 serum run to Nome