Why should people in one part of the globe have developed collectivist cultures,...

Why should people in one part of the globe have developed collectivist cultures, while others went individualist? The United States is the individualism poster child for at least two reasons. First there's immigration. Currently, 12 percent of Americans are immigrants, another 12 percent are children of immigrants, and everyone else except for the 0.9 percent pure Native Americans descend from people who emigrated within the last five hundred years. And who were the immigrants? Those in the settled world who were cranks, malcontents, restless, heretical, black sheep, hyperactive, hypomanic, misanthropic, itchy, unconventional, yearning to be rich, yearning to be out of their damn boring repressive little hamlet, yearning. Couple that with the second reason - for the majority of its colonial and independent history, America has had a moving frontier luring those whose extreme prickly optimism made merely booking passage to the New World insufficiently novel - and you've got America the individualistic.
Why has East Asia provided textbook examples of collectivism? The key is how culture is shaped by the way people traditionally made a living, which in turn is shaped by ecology. And in East Asia it's all about rice. Rice, which was domesticated there roughly ten thousand years ago, requires massive amounts of communal work. Not just backbreaking planting and harvesting, which are done in rotation because the entire village is needed to harvest each family's rice. The United States was not without labor-intensive agriculture historically. But rather than solving that with collectivism, it solved it withe slavery.