Why are there two cities called Kansas City?

There is a city called Kansas City located in the state of Kansas, as one might expect. There is, however, another Kansas City, in the state of Missouri, and it is much bigger than the one in Kansas—in fact, it is the largest city in Missouri. The two cities are separated only by the state border. Why do two different, mutually adjacent cities have the same name? The states of Missouri and Kansas were both...