What was Diamonds intent when he wrote Guns, Germs, and Steel?

In his Prologue to Guns, Germs, and Steel, Jared Diamond clearly states his reasons for writing the book. The most important element of his motivation was to respond to a question asked to him by Yali, a native politician. Yali asked:

"Why is it that you white people developed so much cargo and brought it to New Guinea, but we black people had little cargo of our own?"

Diamond became intrigued by the reasons for the differences Yali noted in material wealth and technological development between the indigenous cultures of New Guinea and the colonizing Europeans. From his personal experience, he knew that natives of Papua New Guinea and other "undeveloped" nations were just as smart and hardworking as Europeans and he realized that older racist claims were untenable and yet the fact of differences in wealth and technology still needed explanation.
Guns, Germs, and Steel reflects Jared Diamond's attempt to discover the original cause of this disparity, which he links to accidents of geography, including the presence of domesticable plants and animals in different regions and how this led to certain areas having earlier adoption of agriculture.