Why did people build most early factories along rivers?

Answer 1

Factories need transportation to bring in supplies needed inside the factory and to ship what is produced in the factory out to stores, the public, etc. Early factories didn't have the use of railroad and trucking transportation, so the quickest way for these early factories to bring things to the factory and ship goods out of the factory was by water. Therefore, they were built along waterways like rivers.

Answer 2

in the old days they learned to use the force of water to power mills: a wheel like a propeller would catch water and the water would cause it to rotate that torque would than be used to power different machines