Why might many people in the southeast culture area have been farmers?

Most of the people in the Southeast culture did tended to be farmers, and the reasons for this are very simple:

- Climate; the climate was excellent for farming, warm and moist for most of the year, with more than enough precipitation and sunlight.

- Soil; the soil was very fertile, which was enabled by the deposits made every year by the rivers, and also because the climate was perfect for quick dissolving of the biomass which is essential for creating a fertile layer of soil.  

- Water; apart from the high amount of precipitation, there's also lots of rivers in this part that were enabling that the plants can be watered all year long.

- Agricultural cultures available; the agricultural cultures that were native for this part were highly demanded and very profitable, which of course was a big stimulation for large scale farming.

the increased occurrence of polygamy

a. factors that are used to make goods and services