Aeg is going to destroy the Stormlands and the Reach.

[a knight of the vale]

The stormlands and the reach are aside from dorne and the vale, the only two regions yet to be destroyed, the riverlands were done away with by tywin lannister, the north is in its own war,the west got it from robb stark, the crown lands did take damage but parts of it remain unscathed (the area nearest to KL). Not only that but these two regions (stormlands and the Reach)are the only ones that can provide food for the rest of the realm. the vale can't because it is isolated, you cant cross the mountain to the riverlands due to it being it winter and the moon tribes, the sea is the path out, but winter has made this dangerous as well. Dorne doesn't have the resources to do so. Now the stormlands and the reach lacks these issues.

But Aeg has landed and the fact a tyrell host will meet them, but seeing Randal Tarly attempted to discredit Connington as a threat, and his wife is heir to brightwater keep following the Florent line of succession, Aeg may find himself with a new ally, but what happens to the tyrell part of the host that lies loyal to mace tyrell whose daughter is wed to Tommen, faced with this issue tarly will butcher the Tyrell loyalist under his command, and declare for Aeg. Now Mace Tyrell is going to fight his former bannerman, bringing war to the Stormlands, he will also have his sons in the Reach bring fire and steel to Tarlys at horn hill and whatever house is allied with them, in the process throwing the reach into a civil war which is already has the iron born to deal with, thus destroying it in process.

Now what if Mace tyrell is the one leading the host, he could fight Aeg, but Mace is a opportunist, he will see an unmarried king, his daughter marriage to tommen has yet to be consummated, he may offer the power of Highgarden in return of Aeg marrying Margery. doing so he will become a enemy of cerise, who is the lady of casterly rock and tommens regent, will go to war with Mace Tyrell. using her power she will unleash what forces she has on the stormlands and the reach, turning the regions into the riverlands, the final move to truly starving the realm( excluding the Vale and Dorne).

[rejndjer]

only problem with 3rd paragraph is that afaik cersei doesn't have any forces any more, what's left of lannister host is controlled by daven(not too sure about this), and they are bringing riverlands in to order, while the rest of the levies returned home to plow the fields.

since martin said throne will change its seater many times in upcoming books it's safe to conclude tommen and cersei are gonna get roast pretty soon, without any un-neccessery fights in south.