It really can't. Sorry, I don't mean to pick on you, it's just that this was a subject of a lot of confusion yesterday and Boney had to make a lot of clarifying remarks. It was doing really well in the voting for a while yesterday because people interpreted it the same way you did, that it would help with the elf-dwarf issue, but it turns out that's not what the trait is for. Here's a particular Boney quote that should be illustrative:
Trucemaker is a trait for "we didn't come out here to fight these guys, let's cut a deal and move on." It is not a trait for getting two other people to get along. That's not something we did during the Expedition.