1. There were actually parts of several states in the Dakota territory: the two Dakotas, Montana, Wyoming, Idaho, and Nebraska. Over time, it fragmented into the boundaries we now know, including the final split when the two halves gained statehood on Nov. 2, 1889.
2. The states are (and were) quite different, despite the many similarities they share. While both have a strong foundation in agriculture, North Dakota has large stores of coal and oil, while South Dakota has gold. Over time, North Dakota has remained largely agricultural, while South Dakota has diversified into retail, finance, and health care.
3. The territories' population clusters (Fargo and Sioux Falls) were located hundreds of miles from each other, and it made more sense from an administrative and logistical standpoint to split them in two.
4. The Republicans lobbied for the inclusion of two states rather than one, as the territory was (and is) firmly Republican, and they were looking to augment their forces in the Senate.
I know you're just trying to be a dick, but it offends me as a native South Dakotan who is proud of his origins and home state, and I'm not going to let you do it.