There's a lot that's not explained about the wards failing all over the world in CRoT. The most obvious question is how; most people agree that the DO is behind it, but whether he is using his servants to unravel them, beating at them with the TP, or causing them to decay by being there is unclear.

A question we might be able to answer is why. Obviously, the DO wants to free up his servants to go anywhere and spread havoc, chaos and death, but why would he attack the wardings in particular? I think that it is to allow SH (DO incarnate?) access to the entire world, particularly the White Tower, the Stone of Tear, and Egwene's camp. We know that the WT was warded against rats and that Alviarin is amused that no one seems to have noticed; if it was also warded against shadowspawn (as seems likely), then the DO might have been forced to destroy these wardings to allow SH access to the WT.

Just as a side note: have the wardings on the Great Hold also failed? If so, in book 11 will we see a forsaken wielding an angreal taken from there? What about the angreal and sa'angreal in the WT--have those been stolen? The failure of the wardings is going to create some major problems in the next few books.