Sometimes strange borders hide in plain sight. According to Wikipedia, there are ten US states with panhandles. Florida, Alaska and Oklahoma are probably the most obvious examples. Every panhandle has a story but none that were defined almost entirely by the fight over slavery.
If fault is to be placed on Oklahoma’s geography, it should be on the US Congress rather than on the state itself. In reading Mark Stein’s excellent book, ‘How the States Got Their Shapes’ I was amazed at just how often the issue of slavery became a determining factor in the definition of the United States, what we now take for granted as, “the land of the free”. Slavery was never an accepted practice in Maine and you can’t get much farther North of the Mason-Dixon line than Maine. But being a free state interested in joining the Union, it had the potential to tip the balance in Congress in favor of a movement against slavery. So Congress tied it’s fate to that of Missouri, a pro-slavery state and allowed both to join the union in the Missouri Compromise. But that act also set a new northern limit for slave states at 36º 30’, a line that would eventually become the southern border of Oklahoma’s Panhandle. Slavery was such a strong motivator at the time that Texas was willing to give up territory to remain a slave state. Mark Stein describes it this way,
“When… Texas entered the Union in 1845, it wanted to maintain slavery, which it had permitted during its days as an independent republic. Under the Missouri Compromise (1820), however, Texas could not be a slave state if it’s borders extended north of 36º 30'. So Texas lopped off its lands north of 36º 30' and gave them to the United States. In doing so, Texas created what would later become the southern border of the Oklahoma Panhandle.
The Kansas-Nebraska Act was passed in 1854, and repealed the Missouri Compromise. It was passed to open up the western territories to settlement but left the issue of slavery open to the settlers of those territories. It also set one of the borders of these settlements at 37 degrees and in the process also set the northern border of what would be come Oklahoma."
The passage of the Missouri Compromise inspired Thomas Jefferson (ironically a slave owner himself) to write the following in a letter to a friend,
"A geographical line, coinciding with a marked principle, moral and political, once conceived and held up to the angry passions of men, will never be obliterated; and every new irritation will mark it deeper and deeper." — Thomas Jefferson
Sources: ‘How the States Got Their Shapes’ , Wikipedia