Mike, treaty or not, we'll just have to agree to disagree. Spoils of war are thousands of years old, and what Poland may say is stolen, Germany will say it wasn't. Germany has that right, as they ran the country after the invasion, and this was a weapon that was seized. It would be the same as anything the US took, while in the countries it has invaded, and that has been a few of them. Any country will say it was legally seized instead of stolen when it's them. Seized meaning they made it their property. The same thing goes with anything the US seized from Germany too.
The legal pirating, I mentioned, has nothing to do with native Americans, as it has to do with pirating on the high seas, that our own government allowed certain shipping companies to do from the east coast harbors. They would board ships from Britain and France, take the loot, and sell it at auction once back at the harbor in places like Baltimore, etc. The US government issued a legal license for them to do it. Now, if those countries want it back, who will they take it from, the ones who legally purchased it at the port, and then on down the line until today, or the US government?
The same goes with the travesty of the folks that found treasure down in the keys, and was forced to give back to governments who hadn't even tried to look for it beforehand, and considered it lost, plus was paid back for it already, years ago, by the insurance consortium's like Lloyd's of London.
Last, why doesn't Poland want any other weapons back, that were seized by the Germans, or Russia for that matter? It's not so much historic, truly, it's because of the worth of it, and they want it. If it has worth to them, then it has worth to the guy who legally had it, too. If it had been legally stolen, I would say send it back, but it wasn't.