They are when you're conquering your neighbors. Massive Roman expansion led to a huge influx of slave labor. When Rome stop expanding the number of incoming sla

They are when you're conquering your neighbors. Massive Roman expansion led to a huge influx of slave labor. When Rome stop expanding the number of incoming slaves decreases and the value of slaves went up. Later on when Rome was hit by plagues they suffered from a lack of laborers to work the fields and staff the army. (Basing this all on the history of Rome podcast)