Help! Did they steal my article?

I must say first of all that I know nothing whatsoever about print media, but I do write regularly for radio. And with my radio pieces, I keep the copyright to my pieces, but sell to the radio station the right to re-broadcast the piece as often as they please (for which right they wil pay me a repeat fee whihc is lower than the original fee). I have had secondary broadcasts of programmes Ive written from other stations, and they then pay me half or a third of the original fee I received in due course. This - with German public rardio stations - is standard procedure.
I would assume that mebbe the same thing applies to newspapers.

Probably best to check with your editor with the Xtian Science Monitor, and if s/he doesnt know anything about it, then I would contact the other paper and ask them how they came by it.

Check your contract. See if you sold your reprints rights to the article.

First, as Chaos asks, what rights did you sell? First rights only? All rights? Also, is Tri State Monitor owned by the same company as the Christian Science Monitor? If so, check your contract to see if you sold the rights exclusively to them or if there is a clause in there about all publications of company xyz being able to use the article.

Another possibility is that the CSM is a member of a syndicate or wire service. Sometimes articles published in one syndicate newspaper are picked up by others. I used to write a column for a small, regional paper that was often picked up by papers in big cities.

Sounds like you need to learn a whole lot more about what you're supposedly doing as a writer.

You don't say anything about the attribution (or lack of it) in the TSM reprint.

You don't say whether you sold the article to CSM with their understanding that it could be (within limits) syndicated.

If this is indicative of how you intend to conduct business, you should look into the NWU or AG or someone who can introduce you to subsidiary uses & the nuances of work-for-hire in the newsroom.