Tranquill have long been seen as a symbol of peace – a symbolism which is today often forgotten, because much of humanity has forgotten that peace has a horrific, tragic alternative. Back when war captured mankind's attentions and lives, however, legends abounded about the Tranquill, on whom people projected their hopes for a life without such massive bloodshed.
Perhaps these legends have their origins in the fact that many of Tranquill's techniques make them supremely difficult targets in wars, or from the tales that some flocks have used featherdance on warring armies en masse in the hopes of making further killing impossible. Or perhaps it is because Tranquill are among the least fractious of pokemon; when given the choice between fight or flight, they universally trust in the ability of their wings and their navigation skills, which are as advanced as a Pidove's are poor, to find themselves a new home. This solution to conflict, to be sure, is known to humanity, but in eras where arable land was scarce and exile a punishment more often than a choice, many people looked upon the Tranquill with envy. In times of famine, some would take advantage of their pacifism to raid Tranquill nests for food, but most condemned those who took this step for it was robbing the righteous.
Because Tranquill so abhor war, armies did not fear them as invaders, spies, or even enemy messengers, and they were viewed as innocent of all violence. Consequently, any Tranquill, no matter their owner, could be guaranteed safe conduct through warring lands. This fact, combined with the dangers of more conventional diplomacy, evolved into a custom of negotiating ends to particularly bitter conflicts not face-to-face, but by messages attached to these pokemon's legs; a custom which survived until Tranquill negotiation ended Unova's final war.