Honey War
The Honey War was caused by a disagreement over a  wide piece of land covering the entire border (see map).  The disagreement was caused because 3 things were not easy to understand: the Missouri Constitution's part about borders, the survey of the Louisiana Purchase, and treaties with the Native Americans.  The United States Supreme Court ended the dispute in Iowa's favor.  It said that the almost-straight border of Iowa would follow the Des Moines River south for about  until it reached the Mississippi River near Keokuk.