The Rule of the Commonfolk

Origins
A few years before the death of King Bran the Riverlands Kingdom was reformed into the Trident Union by the Brotherhood without Banners, heroes of the common people during the War of the Five Kings and now the heralds of a new regime led by Joseph Dondarrion, who deposed the Great House of Tully but not before they were rescued and put in hiding by Beric Dondarrion II. After the Slaughter at Harrenhal where both the Crusader State of the Crownlands and the Trident Union destroyed most of if not all of eachother's forces, the Trident Union was forcefully dissolved by Lord Beric and House Tully was restored to their seat in Riverrun. This did not cause the idea of a kingdom ruled by the people to go away as it was remembered fondly by the Riverlander peasantry and smallfolk.

Historic Impact
After the Second Clash, the commonfolk were on the rise again because of the destruction the final battles of the war had brought to the Kingdom. Instead of fighting bloody wars, like the lords of the First Clash had done to stop the ideology, Stannis Baratheon II chose to appease them, and kept the peace. This secured the Riverlands during his reign but allowed the commonfolk to spread their ideals beyond the Riverlands, which some would say was only a matter of time.

This resulted in a historic moment during the Third Clash where Lord Arryn, hero of the people, found his end in King's Landing in the explosion from the Second Sept of Baelor where he was giving a religious speech to a large crowd of commoners. Begriefed at his violent assassination, the people of King's Landing rose up in rebellion against the Great Council. This nearly resulted in the declaration of an independent King's Landing ruled by it's own citizens in total equality with help of Lord Arryn's son who almost stormed the Red Keep. The massive riots that marked this event however made this impossible and the new Lord Arryn had also found his end in the Capitol. The Great Council members that remained in the Capitol were nearly torn to shreds but made a narrow escape. This allowed them to regroup and continue the mistake both Bran the Broken and Stannis the Kind had made, which was appease even more than ever before seen.

A peasant with a very loud voice was nearly named Lord of the Vale in order to usurp the House Arryn from their seat. Luckily he was only named Master of Soup for the small council. What this new Master of Soup was supposed to do wasn't entirely clear to everyone involved but it gave the commonfolk an officially recognized voice that would advise the next monarchs. The plan to hand the Vale to people was still enacted by the Great Council and House Arryn lost their ancestral seat, making the Vale the second kingdom ruled by the common people.

Whether the new king and queen realised what their actions meant by giving commoners massive influence in both the Vale and Crownlands alongside the remnants in the Riverlands is still up for debate by scholars. It will most likely play a big role in the wars to come.