Chenbao and the Northern Passage are a canon-era flashpoint: a raw border after an earlier tsunami-and-tax crisis. In 12 BG the wound has not healed. Governor Pei [Original] sits in the Governor's Keep, tax hall overlooking the Passage, with coastal batteries and disputed waters below. He stamps cargo that should not move. Polar ships and Earth batteries stare at each other.
WHY IT MATTERS NOW
Roku is gone. There is no Avatar to mediate a coastal crisis. Prince Tulok in Agna Qel'a is closer to a war footing than the healers want. Chief Skiri wants dignity without a reckless war. Pakak, at Northfat and Bone, has seen forged stamps from the Passage. Ships return to Agna Qel'a with contraband marks and spirit-sickness. Captain Nukilik holds the frozen gates. Ferryman Taktuq can carry a warning that should not be written down. A regional war here is exactly the kind of cover Sozin can use in year 1 of the clock. "If ignored: a regional war gives Sozin cover" is not flavor. It is a possible campaign failure state that still leaves eleven years of worse decisions.
HOW TO PLAY THE PASSAGE
It is not a simple good tribe versus evil governor cartoon unless the table pushes it that way. Pei may be a tax official in a frightened Earth Kingdom that lost work and coastline in a disaster and wants revenue. Tulok may be right that the stamps are a weapon. Both can be used by Mandate cargo, Omashu rumor, or Ba Sing Se neglect. Yuanli will call it an outer matter. The Northern Air Temple, with Youdron and Jamyang, can see the Passage from mountain landings and may be asked to mediate while their own children are being tested.
QUESTLINE: PASSAGE TO WAR
Start at a gate, a ferry, or a stall: Nukilik, Pakak, Taktuq, Iqaluk's sick guest, or a battery officer under Pei. Follow a stamped crate, a sick sailor, a forged seal, or a cutter that is not where it claimed to be. End in a conclave, a diplomatic climb-down, a spark, or a quiet theft of the next week's tax ledgers. Tie spirit-sickness to hunts and industry if you want the poles and the Passage to be one wound, not two unrelated plots.