Machine guns, poison gas, tanks!
Most likely because in poor, rural areas, public schools are scarce/ not easily available, and so sending a girl to school is not as prioritized as sending a boy to school, since a boy can start working and be a "breadwinner" for the family sooner than a girl.
The Americans were huge areas of fertile land, and the European powers needed people to work on its fields. African slaves were a cheap and abundant solution.
