Crazy theory of the moment - following what happened to Hodor, does anyone think that Bran caused the Mad King to go crazy? Except that when he said "Burn them all", it wasn't a reference to the people of King's Landing but instead the Wights?
No. Aerys had caches of wildfire hidden all over the city in case it was invaded, and previously he had Ned Stark's father, Rickard, burned too. So he was a confirmed murderous, pyromanic lunatic already.
Season 1:
Jaime: When I watched the Mad King die, I remember him laughing as your
father burned. It felt like justice.
Ned: Is that what you tell yourself at night? You’re a servant of justice?
That you were avenging my father when you drove your sword in Aerys
Targaryen’s back?
Jaime: Tell me, if I stabbed the Mad King in the belly instead of the back,
would you admire me more?
Ned: You served him well when serving was safe.
In Season 3, Jaime to Brienne:
You all despise me. “Kingslayer. Oathbreaker. Man without honor.” You
heard of wildfire? The Mad King was obsessed with it. He loved to
watch people burn. They way their skin blackened and blistered and
melted off their bones. He burned Lords he didn’t like, he burned
Hands who disobeyed him. He burned anyone who was against him. Before
long half the country was against him. Aerys saw traitors everywhere,
so he had his pyromancer place caches of wildfire all over the city.
Beneath the Sept of Baelor and the slums of Fleabottom. House,
stables, taverns. Even beneath the Red Keep itself.
Finally, the day of reckoning came. Robert Baratheon marched on the
capitol after his victory at the Trident. But my father went first
with the whole Lannister army at this back promising to defend the
city against the rebels. I knew my father better than that. He’s never
been one to pick the losing side. I told the Mad King as much. I urged
him to surrender peacefully. But he didn’t listen to me. He didn’t
listen to Varys who tried to warn him. But he did listen to Grand
Maester Pycelle—the great sunken ****. “You can trust the Lannisters,”
he said. “The Lannisters have always been true friends of the crown.”
So he opened the gates and my father sacked the city. Once again I
came to the king begging him to surrender. He told me to bring him my
father’s head. Then he turned to his pyromancer. “Burn them all,” he
said. “Burn them in their homes, burn them in their beds.”
First I killed the pyromancer and then, when the king turned to flee,
I drove my sword into his back. “Burn them all,” he kept saying. “Burn
them all.”