What was the primary reason that separate, early villages first began to cooperate with one another?

To create a unified military defense against invaders

To build and maintain large-scale irrigation systems

To establish a common currency for trade

To elect a single ruler for the entire region

In the context of early irrigation, what problem was caused by the buildup of silt?

It made the surrounding farmland less fertile.

It attracted dangerous animals to the water sources.

It clogged the canals and blocked the flow of water.

It required farmers to invent entirely new types of plows to till the soil.

Deciding crop rotation schedules for all farms

Find a better location for hunting and gathering.

Work together to manage shared water resources.

Build large defensive walls to protect a single sacred site.

Create a central marketplace for international trade routes.