According to Guns, Germs, and Steel, in what ways did a centralized government provide strength to early societies?

To see why a centralized government is useful, look at
Diamond's description of the Fayu at the start of the chapter or look at the biography
of the Iyau woman on p. 277 in the paperback edition.  In both of those passages, we see
that societies without centralized government have a hard time providing their people
with stable lives.

As societies grow larger, they need
governments.  They can no longer be held together by family ties.  Someone needs to have
the authority to do things like preventing people from killing one another.  This is
where government comes in.  Government strengthens societies by creating ways for large
populations to live together in peace.

Of course, there are
problems that go along with having a centralized government.  However, a society without
such a government, like that of the Fayu, is one that is very unpleasant and dangerous
to live in.