Why is reaching Stronghold Tier 10 before the Reign ends important?

A costly mistake: letting a Reign end without having reached Tier 10 on your Stronghold.

Stronghold Tier 10 is required before the Reign ends to claim the campaign rewards. The "Heirs of the Dragon" campaign runs 11 chapters plus an epilogue, takes around 40 days, and demands exactly that Tier 10 Stronghold to be completed.

So, at the start of a season:

1. Re-grind your Stronghold Tier quickly (it reset).
2. Keep an eye on the campaign progress and its objectives.
3. Don't drag your feet: 40 days go fast when you also have dragons and armies to raise.

Missing Tier 10 means leaving rewards on the table that you'd almost earned. Plan your season around that goal.