In the Game of Thrones finale, we see
the Lords of Westeros declaring Bran King of the Six Kingdoms (Sansa declared the North an independent entity).
However, with an era of peace on the horizon and with
the Unsullied leaving Westeros and the Dothraki presumably doing the same/disbanding
there doesn't appear to be any power exclusively behind the monarchy. It makes sense for some of the weaker Lords to agree to a ruling monarch, but a few of the Lords have formidable standing armies; certainly stronger than anything the monarchy now has.
It seems to me that having the sole ability to rule your own land and having no monarchy to pay taxes/owe troops to would be in an individual Lord's best interest. With no significant threat of war and no power to enforce the monarch's rights, what would prevent the strongest Lords from following the previous example of
and declaring independence?