How did wild mustangs become endangered?

Wild mustangs were persecuted by ranchers for taking over grazing lands that were intended for their cattle. As a result, large numbers were rounded up and taken to the slaughter plant to be made into glue and dog food. Also, a lot of their habitat had been exploited and taken over by humans, driving them into smaller-sized isolated areas where they can only thrive from. Wild horses are almost like wolves: they thrive best where humans are not living or are commonly found. They prefer very isolated areas that are literally untouched by the encroachment of human civilization.