A mad queen sits on the Iron Throne, the White Walkers are through The Wall, and Ser Pounce is dead.
Things aren't exactly stellar in Westeros right now, and with winter here they could get a lot worse real soon. Like, "eternal darkness" worse.
Things didn't have to be this bad in the Realm, though. Lots of important players have made terrible decisions that have had catastrophic results. If they had only handled a few choice crossroads a little differently, the living might be in much better shape to take on the dead now.
Here are the eight worst decisions made on Game of Thrones that have led them to this perilous spot.
Jon Goes Wight Hunting Beyond the Wall
In Jon's defense, offering tangible proof the White Walkers exist seemed to be the only way to a) get the warring factions to accept the threat was real, and b) get everyone to work together. (Those in power had been foolishly ignoring Jeor Mormont's warning letters for years, another huge mistake.) The problem was that going beyond the Wall with a small (horseless!) group, to capture a single wight from an army 100,000 strong, was insanely stupid. It was a dumb idea on its own, and then it ended with the Night King having his very own dragon, which might make him too powerful even for a unified army of the living. Not great!
Robb Marries Talisa (Then Trusts Walder Frey)
Everyone knew Walder Frey was a vile man who couldn't be trusted, but Robb still broke his sacred vow to marry one of his daughters. It cost the King in the North a valuable and needed ally (which he missed even more after foolishly executing Rickard Karstark rather than keeping him hostage, costing him another vital force). Robb's wedding and desperation led to an even worse decision.
The Starks were only at the Red Wedding because they were hoping to bring the Freys back into the fold. Trusting that angry old man didn't just end with Robb and Catelyn's death; it led to a fractured North under the Boltons, a stronger House Lannister, and thousands more dead.
Theon Betrays Robb
Theon had a choice: his family or his friend. He chose House Greyjoy, which then attacked while Robb was heading south to face the Lannisters. Theon himself (stupidly) took Winterfell. On a personal level it led to Theon becoming Reek, but on a bigger scale also helped ruin the Starks. If Theon had warned Robb like he'd originally planned, the Starks could have stopped the Greyjoy rebellion before it started, and it would have left them less vulnerable to the Bolton betrayal. A strong North, with many of its best soldiers still alive fighting under King Robb (who might have defeated the Lannisters), would have made a huge difference in the Great War.
Renly Splits the Baratheon Forces
Following Robert's death, Stannis was the rightful heir. Instead, his younger brother Renly, without any claim, decided he should be king instead. He split the family's combined forces at a time when a united House Baratheon could have crushed the Lannisters. This led Stannis to kill Renly with a shadow baby, giving him a bigger force when many of Renly's men came back to his side. Unfortunately it sent a grieving Loras and the incredible power (and food) of House Tyrell to align with the Lannisters (although that ended up being a horrible decision too). That new alliance decided the Battle of Blackwater, keeping Westeros in a civil war for years at a time when it needed to turn its focus beyond the Wall.
Ned Confronts Cersei
A less honorable man would have arrested Cersei, Jaime, and their illegitimate children when he discovered the truth about the family. Instead Ned opted for a private conversation with the most dangerous woman in the world so she could flee Robert's wrath. While well-intentioned, it was a monstrously shortsighted/dumb decision that endangered his own family and plunged Westeros into war. It also led to a number of other horrible decisions, like when Ned trusted Baelish to help him secure the City Watch's loyalty, and when Joffrey executed Lord Stark when he was a hugely valuable hostage. Ned was the greatest man who ever lived, but he still made arguably the show's worst decision.
Catelyn Arrests Tyrion
This is really a two-fer, because it also involved Catelyn trusting Baelish (duuuumb). Littlefinger lied and said the dagger used to try and kill Bran belonged to Tyrion (after she believed Lysa's lie that the Lannisters killed Jon Arryn). None of that was hard proof, and even if it were, Catelyn should have done nothing when she came across Tyrion on the King's Road.
By arresting him, she showed her unfinished hand and declared war on House Lannister. That led to Jaime confronting Ned in King's Landing. When Ned lied to protect his wife by saying he ordered Tyrion's arrest, Jaime attacked Ned's men. The war between the Starks and the Lannisters has been a catastrophe for both houses and the Realm.
Jaime and Cersei "Meet" in Winterfell's Broken Tower
This could also be titled "Bran Goes Climbing," since his mother did forbid him to do it. However, there wouldn't have been any problem for Bran if the incestuous twins hadn't decided to cavort in Winterfell. It was dangerous, selfish, and stupid, and it led Jaime to push Bran out the window, which was the precursor to the Stark/Lannister issues that would soon explode. In an alternate timeline where Bran isn't crippled, he might never go beyond the wall, foolishly enter into a vision alone, be marked by the Night King, and get the original Three-Eyed Raven killed.
Rhaegar Chooses Lyanna
Long before the show started, another decision borne of love set everything in motion for the story we know. At the infamous Tourney at Harrenhal, the Crown Prince Rhaegar Targaryen passed over his wife to name Lyanna Stark the queen of love and beauty. Her "kidnapping"/secret marriage led to Robert's Rebellion and an unstable, fractured Westeros, which ultimately broke apart years later thanks to Cersei and Robert's loveless marriage.
Rhaegar was wise, brave, beloved, and likely to unseat his father, the Mad King, soon. Under him the Seven Kingdoms could have prospered and been ready to face the White Walkers before they grew so powerful. Instead Rhaegar chose love over duty. It led to his death, the near destruction of his family, and it may have doomed the living to eternal death and darkness.
It's hard to come up with a worst decision than that. But at least giving birth to Jon Snow was a good idea.