The tree grows old, as trees do: old and brittle. Branches crack and fall, and with them thousands plummet to their deaths. When there is no rain we bring water to the roots to keep the tree healthy as long as possible, but we know we fight a losing battle; soon we will need a new home.
There are other trees. Some are not yet occupied, but all are claimed. Any move will mean war. We have few soldiers but many flyers, so if the issue is decided in the air we may have a chance. We have no choice.