Select all that apply. Three possible reasons for the expansion of smaller kingdoms are .

The grass is greener elsewhere.
A larger population requires more food.
Leaders are greedy for more power and land.
Neighbors are becoming too strong.
It is better to be larger than smaller.

The correct answer is -

Leaders are greedy for more power and land,

It is better to be larger than smaller,

A larger population requires more food.

Explanation:

The possible reasons to expand smaller kingdoms are can be numerous. It includes an increase in the population requires more resources such as food and land, greedy leaders that run for the power and land to be strong than their neighbors.

The third important reason could be  simply an expansion of the state for more resources or that larger kingdoms have fewer chances to get attacked by the other kingdoms

this null effect is caused by a weak manipulation and ineffective internal validity. in a scientific study, as the one dr. morimoto is trying to perfom, internal validity refers to the confidence placed in the cause-effect relationship and to how well an experiment is done and able to eliminate confounding variables.