1. On May 13, 1846, the United States declared war on Mexico, which had significant consequences for Iowa. Because of the war, many soldiers and volunteers traveled through Iowa Territory en route to Mexico, and Iowa also played a significant role in supplying troops and resources for the war effort.

2. May 13, 1871, saw one of the worst tornado outbreaks in Iowa history, as a series of powerful tornadoes tore through several counties in the state, killing dozens and causing widespread destruction. The event still holds the record for the most tornadoes recorded in Iowa on a single day.

3. In 1884, on May 13, a group of Iowa farmers formed the Farmers' Alliance, which was a precursor to the Populist Party. The Alliance was a response to farmers' struggles with economic adversity and the perceived exploitation by railroads and other corporations. It was a major player in Iowa politics for several decades.

4. On May 13, 1934, notorious bank robber Bonnie Parker and her partner Clyde Barrow were killed in a police ambush near Gibsland, Louisiana. The couple had a connection to Iowa, as they had stolen a car in Kansas City that they later abandoned in Clarinda, Iowa, while being pursued by law enforcement.

5. May 13, 1998, was a momentous day for the Iowa LGBT community, as the state Supreme Court ruled that denying a gay couple a marriage license was unconstitutional. The ruling paved the way for Iowa to become the third state in the country to legalize same-sex marriage, when it did so in 2009.