CFTC's guidelines around prediction markets specifically call out war outcomes.

"As a general matter, DCMs are reminded that section 5c(c)(5)(C) of the CEA provides that the Commission may determine that an event contract is contrary to the public interest if the contract involves, among other things, assassination, war, or terrorism."

The guidelines are at https://www.cftc.gov/csl/26-08/download

If I worked at Amazon, "AWS outage by ... date" bets on Polymarket would look mighty tempting.