Answer:
Because people were forcefully taken away from their home countries to another country entirely for slavery.
Step-by-step explanation:
Chattel slavery is a forced diaspora "because people were forcefully taken away from their home countries to another country entirely for slavery." This was common during the trans-Atlantic trade which involves mass transportation of enslaved people from West Africa and Africa in general to America around the sixteenth century to the nineteenth century.
In other words, through chattel slavery, enslaved people were taken to another land without their consent. Thereby constituting "Forced Diaspora."