You have to complete all the main missions and strongholds to have the map convert to World Tier 1 and the Black Tusk have retaken most everything.
Just finished all the WT Strongholds and now at World Tier 4. Power level to 417 and I need to get that to 450 for the upcoming Tidal Basin (after defeating you unlock WT5) and I think you them can upgrade to 500 Power Level.
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