Missouri town gained by America in 1783 (12)
I believe the answer is:
independence
'missouri town' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'america in 1783' is the wordplay.
I cannot really see how this works, but
'in' is within the answer.
The remaining letters 'dependence' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'gained by' acts as a link.
Can you help me to learn more?
(Other definitions for independence that I've seen before include "Freedom from outside control" , "lack of bias" , "Freedom from another's authority" , "Autonomy" , "Self-reliance" .)