Rhaego did not want to worry his mother, but he had already decided that he would resolve the problems that his mother was too weak-willed to take.
Slave Bay was not Westeros, and her reform was much more difficult to pass here than it was for Aegon to unify most of Westeros because Aegon practically did not change anything about how the continent politics works, while Daenerys was attacking the very foundation in which power works in this region, so being ruthless was the only logical choice in Rhaego opinion. He was a Targaryen and fire and blood were in his blood.
He flew to Yunkai, which was easy as he only had to fly slightly northeast following the coast, named Horns of Hazzat. Flying made him able to reach his destination much faster than any horse could, so before the news of the Astapor sack even reached Yunkai, he attacked the city, pulling a 'Blitzkrieg' at his enemies.
Yunkai is made of yellow bricks, with crumbling walls, towers, and tall, stepped pyramids. These include the golden pyramid of Qaggaz. A great harpy is mounted above the city's gates. The 'wise master' of the city leaves in these beautiful well-defended pyramids, usually on terraces. So this made it easy for Rhaego who started to burn up the pyramids and also the ghiscari temples to leave the city leaderless.
There was a master with a scorpion, not for use against the not-so-long-ago extinct dragons, but merely for collection. But he lacked anyone that knew how to properly use it, so Rhaego only have to burn the thing with the 'wise' master militia, before it was shot at him. Rhaego was careful, however, instead of flying straight he made several maneuvers in the air to avoid being targeted.
Fear was a useful tactic in politics and war, but Rhaego consider it dangerous because if violence and oppression were used without proper measure fear could be turned into blind hatred. He knew that the conflict of interest between his mother's campaign and the slave masters and the ghiscari religion, which basically endorses not only slavery but demands and sanctifies the sacrifice of slaves; was irreconcilable. Playing political games with them was a waste of time, considering Yunkai would restart slavery as soon as Daenerys left their walls.
He knew that a lot of innocent people, including slaves may have died during his attack, but Rhaego, maybe by the influence of his Dothraki blood, was not your idealistic hero who would foolishly try to save everyone, he obviously prioritized the safety of his allies over his enemies.
Yunkai would no longer hire two sellsword companies, the Stormcrows, and the Second Sons, to strengthen their own slave army of four thousand strong. Their slave army was mostly formed by the militia of each slave master, which missed common slaves soldiers and unsullied. Rhaego however has already killed most of them in his previous attack. After Rhaego left, Yunkai descended into anarchy, with slave riots everywhere, pillaging, and the underpaid and corrupt city guard unable to keep control over the situation.
Rhaego flew to Meeren and reached the before any news of the Sack of Astapor and his Yunkai burning reached there.
Meereen is the largest and most formidable of the cities along Slaver's Bay. Meereen is as large as Astapor and Yunkai combined. Like them, the city is made of brick, but unlike Astapor and Yunkai, Meereen's bricks are of many different colors. Meereen's walls are higher than Yunkai's and Astapor's, thicker than Astapor's, and better maintained than Yunkai's, studded with bastions and anchored by great defensive towers at every angle.
The city's north wall runs along the riverbank, it's west along the bay shore. The river wall is a few feet higher than the others. Upon the walls, rows of bronze harpy heads with open mouths are positioned, from which the Meereenese can squirt boiling oil out upon any attacker below. Within the city, there are narrow twisty alleys and wide brick streets, temples, granaries, hovels, palaces, brothels, baths, gardens, fountains, and fighting pits.
The nobility of Meereen lived in the stepped pyramids. The greatest of them all is the Great Pyramid, located on Meereen's central plaza, which stands eight hundred feet tall. There was a score of lesser pyramids in the city, but none stand even half as high. The Great Pyramid has a great bronze harpy on top of its apex.
The pyramids are built in the colors of the noble house occupying them; The pyramid of Pahl was pink-and-white, the pyramid of Naqqan was green-and-black, and the great pyramid of Rhazdar was yellow-and-green. The pyramid of Kandaq was said to be modest. Rhaego turned the bricks of pyramids black and turned them into ruins with his body.
Between the pyramids, the poorer districts are located.
The city's wastes are carried into the Skahazadhan by great brick sewers. These sewers are closed off with iron gates, although some have rusted through. The Meereenese do not drink the water from the river; Instead, they drink the water gathered from wells.
Meereen has multiple fighting pits scattered across Meereen. These include Daznak's Pit, the Pit of Ghrazz, and the Golden Pit. Daznak's Pit is the largest of all the fighting pits in the city. It is located west of the Great Pyramid.
The Temple of the Graces, home to the priestesses of Meereen, was likewise located west of the Great Pyramid. It was a huge structure topped with golden domes, until Rahego burned and smashed it, turning it into a ruin.
Rhaego was also merciless against the Merrenese because negotiating with these people was stupid. In his opinion, Daenerys in the books was too kind to them. After having their lives spared they still did not know their place and started assassinating her unsullied, and she negotiated with them when they were in her hands. Sure there would have been a war in the city, but it was a fight her enemies could not win, and that was the reason they plainly did not revolt but decided to play political cheap games.
A great bronze harpy could be found in the Plaza of Purification. Meereen has several markets, including a spice market where the Purple Lotus is located, near the great pyramid of Rhazdar. Another location in Meereen is Mazdhan's Maze.
There was a market inside Meereen's great western gate. This market square houses Meereen's ancient Slave Exchange, the merchant's arcade that fronts the southern side of the square, and the weathered bronze statue of the Chainmaker. Not far from the statue is the ghastly monument the Great Masters called the Spire of Skulls.
Now that the cataclysm have already passed and Rhaego went away, Meeren had already turned into chaos.