Following the Neolithic Subpluvial, around 7500 to 3500 BCE, the "green Sahara" became dry and the scimitar oryx's population began to decline due to a loss of suitable habitat. This was further exacerbated by humans who hunted the scimitar oryx for both its meat and horns. The northern population was already almost lost before the 20th century. With the introduction of horses and firearms during the 20th century, nomadic hunters were able to decimate populations. The decline of the southern population accelerated as Europeans began to settle the area and hunt them for meat, hides and horn trophies. French involvement in World War II and the civil war in Chad that started in the 1960s are thought to have caused heavy decreases of the species through an increase in hunting for food. Roadkill, nomadic settlements near watering holes (the oryx's dry-season feeding places), and introduction of cattle and firearms for easy hunting have also reduced numbers.