I'm not sure if auto resolve still works to get the event. I don't like using it because you lose more warriors than if you fought it out yourself. I usually do what Soly suggested, use my Daimyo to attack an archer unit early in the campaign. I can usually trigger the event by the second battle if not the first. Just be careful not to expose him to a flank attack by YS's, guard his flank with YA unit, they're fast enough to keep up. Any of his hatamoto bodyguard will be regenerated for free on the next turn, so losing a few doesn't hurt as long as your Daimyo survives.

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Diplomacy is the art of telling someone to go to hell so that they look forward to making the trip.