This started as a Sunday grid I wrote in 2014. I wanted to do a puzzle where opposing forces came at each other from opposite directions. So it had DEMOCRATS (from the left) clashing against SNACILBUPER from the right, etc. No one wanted it, and it sat in my dead puzzles folder until The Puzzle Society opened shop. In the constructor community, we're certainly fortunate that David is so open to unusual ideas. I reviewed a lot of these that had gone unused and liked this one. HEAD TO HEAD is a theme I haven't seen before. Most of the 21x ones were too long, but SNEHTA SPARTA was in there, so I decided to make it all historic enemies. War may be an ugly topic, but each of these conflicts is historically important. I'd be surprised if anyone with the intellectual curiosity to enjoy crossword puzzles is unfamiliar with them.