There are some places in US, that contain "MO" in their names. For example, Columbia, MO; Kirkwood, MO; Saint Louis, MO. So, what does MO mean?
The state abbreviation (such as MO) is sometimes required because quite often there is more than one city with the same name in the US. There is a "Portland" in Maine and one in Oregon; Kansas City, Missouri and Kansas City, Kansas (same city, but the state line runs across the city), and almost each state has it's own "Springfield".