Warning: Spoilers for "Game of Thrones" season seven, episode three, "The Queen's Justice." If you aren't caught up on the series, read at your own risk.
Sunday's episode of "Game of Thrones" ended with an unexpected turn. The Lannister army, led by Jaime, abandoned its home of Casterly Rock and took Highgarden, while the Unsullied fought a small contingent of Lannisters.
In taking Highgarden, the Tyrell stronghold, Cersei manages to completely erase the Tyrell bloodline from existence.
While it might seem like an act of revenge on Olenna and a clever battle strategy at first, it's a lot more than that if you think about what happened earlier in the episode. Tycho Nestoris, a representative from the Iron Bank of Braavos, shows up in King's Landing to discuss the crown's massive debts with Cersei. And it looks like Cersei's plan to take Highgarden has something to do with the Iron Bank.
But what exactly is the Iron Bank of Braavos, and how influential is their power in the events to come? Find out below:
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What is the Iron Bank of Braavos?

The Iron Bank is the main bank of Braavos, and one of the wealthiest banks in the Known World. It often lends money to foreigners, including Lords of the Seven Kingdoms and the King of the Seven Kingdoms. All the Free Cities have banks, but the Iron Bank is richer and more powerful than all of them combined, and is very strict about debts and agreements.
A common saying among the Braavosi is, "The Iron Bank will have its due."
Have we seen it before?

Yes.
In season four, Davos comes up with a clever plan to get a loan from the Iron Bank of Braavos. Stannis and Davos sail to Braavos and meet with Tycho Nestoris and two of his colleagues. Davos wins the loan by explaining that Stannis is the best investment to make if the bank wants the crown's debt paid back — because it doesn't look like the Lannisters are long for this world. Stannis uses the money to re-supply his troops and head to Castle Black, just in time to save them from the wildling attack.
And remember when Mace Tyrell sings his beautiful song in the free city of Braavos in season five? Cersei sent him there accompanied by Meryn Trant to negotiate with the Iron Bank, but it's actually a bribe, which Tycho declines.
What does the taking of Highgarden have to do with all of this?

Pretty much everything, actually.
In season four, Tywin Lannister tells Cersei that one of the reasons he agreed to ally with House Tyrell was its wealth — it could help pay the bank back.
In the same scene, Tywin reveals that the mines of Casterly Rock are barren and have been for years. This little nugget of important information helps Cersei realize that Casterly Rock is of no value to her, despite being her home.
So without any money in King's Landing, Casterly Rock, or from any of her allies — Euron Greyjoy has a lot of ships, leather and eyeliner, but definitely not gold — she has Jaime and his army literally follow the money to Highgarden.
At this point, it's safe to assume that the Lannister army in Highgarden will search the stronghold for gold, and use it to pay the Iron Bank.
See the rest of the story at Business Insider