What is the thesis statement for Part 4 of Guns, Germs, and Steel?Just for Part 4, not for the whole book.

Part 4 of this book includes five chapters that touch on
every populated continent on the globe.  Because of this, there is no single explicit
thesis statement that covers the whole part.  However, there is at least one sentence
that comes close to summing up Diamond's major thesis that he is trying to prove over
the course of these five chapters.

This sentence comes at
the end of Chapter 19.  There, he tells us that European domination of
Africa

was due
to accidents of geography and biogeography--in particular, to the continents' different
areas, axes, and suites of wild plant and animal
species.

If we discount the
fact that this sentence is specifically about Africa and Europe, we can use it as a
thesis statement for the whole part of the book.  This is particularly true of the first
part of the sentence.  In Part 4, Diamond is trying to prove that it was "accidents of
geography and biogeography" that determined which people were to dominate the world and
which were to be conquered.