It usually takes teamwork to create projects, and teams can squabble, but as long as there is communication the project can still be completed. Diverse teams means accepting differences, liking everything about someone isn't necessary to work together, Civilizations are built by groups who manage to work together whatever their differences may be.
Civilizations that collapse tend to have become divided and are no longer working towards the greater good - such as food production and waste removal. Civilizations that collapse also tend to be those that have grown too large for the surrounding area and food production and waste removal needs are not being met for the greater number of people living in the urban settlements. Climate change and natural disasters can also negatively affect civilizations, hostile neighbors and whether a group is participating in trade can also be factors that help a group survive or collapse.
Adapting creatively to changes in the environment and changes in the population are what helps groups survive.
For more information on the history of many civilizations, their decline and collapse see: Collapse: How Societies Choose to Fail or Succeed, by Jared Diamond (jareddiamond.com).
Review of Collapse by Jared Diamond: Man vs Nature, by Jonathon Porritt, (theguardian)
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