Question

What was the key element that led people to settle in agricultural lifestyle

Answer 1

I think the key element would be knowledge and science 
the hunting and gathering method created several problems in early human civilizations, such as :
- hard to find food on winter
- Group was expose to various dangers and have to continually moving

To solve this, we created agricultural method, so we can stay in one place and stock up our food on winter

hope this helps