How is organizing the past by the theme different from organizing the past by region

Humankind as a whole has a history that can be described and in some measure understood. Studying the human past in a holistic way means asking historical questions about events and developments that are relatively broad in time and space. Investigating the past on any scale is valid. Where one scholar might research 30 years in the modern history of a Mexican village, another might take on 300 years in the development of Latin American economies. A third might explore 3,000 years of global climatic change and its affects on economic change around the world. A fourth might consider why human beings took up agriculture in the context of 300,000 years of human biological and cultural development.