As the Foundation has grown, more and more power and wealth have accrued to non-Terminus traders. One of these, Hober Mallow, is sent to Korell to determine why other Foundation ships which have gone there have vanished. He manages very well, discovering that Korell’s military is being underwritten by an ambitious Imperial viceroy.
On return to Terminus, however, he’s put on trial for allowing a Foundation missionary to be lynched and is nearly convicted. He proves, however, that the “missionary” was really a Korellian spy and with the triumph of his aquittal becomes Mayor and brings a brief war with Korell to a satisfactory conclusion by simply cutting Korell off from the economic benefits of trade with Terminus.
This is not, perhaps, one of the best Foundation stories, but it is definitely one of the better ones.
One historical note. “The Big and the Little” was actually written and published before "The Traders,” but when the original Foundation stories were collected in book form, the latter (and weaker) story was placed first—a much more felicitous arrangement.