conjunction
BAD : Although I enjoyed my stay in the USA, but I was still glad to come home.
GOOD : Although I enjoyed my stay in the USA, I was still glad to come home.
GOOD : I enjoyed my stay in the USA, but I was still glad to come home.
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If the first clause begins with although or (even) though, do not begin the second clause with but or yet .
See also SO 2 (↑ so )