Complex sentence: Throughout French West Africa almost a million slaves responded to this by moving away from their masters and settling elsewhere, with the French supporting this effort by creating settlements around the Niger River and digging wells for communities elsewhere to engage in agriculture away from their former masters.
Split into simpler sentences: Throughout French West Africa, almost a million slaves responded to this by moving away from their masters and settling elsewhere. The French supported this effort by creating settlements around the Niger River and digging wells for communities elsewhere so they could farm away from their former masters.