If by "recruit" you mean enslave thousands of people and force them to work on building siege machines and digging tranches than yes :)

Seriously, I've read that each Mongol warrior was supposed to catch like 10 people as they moved through the invaded lands and they would move all those people like cattle with the army. When they finally reached the main objective they would force all those people to cut down trees and build siege machines. People from smaller towns would flee the incoming army to bigger forts which meant that before Mongols got there the cities were already overcrowded and had troubles to withstand the siege. It was methodical and brutal and worked perfectly.