The name possibly covered a larger area in the past, as evident by the existence of a province in Afghanistan called Zabul at the foot of the Hindukush, (along the border with Pakistan). According to Persian mythology, Zabulistan was the country of Iranian hero Rostam. In Shahnameh, Zabulistan and Sistan are used interchangeably.
In ancient times, Zabulistan was part of the region known as Arachosia. Northern parts of the region were under control of the Medes Empire before 550 BCE, after which the province fell to the Achaemenid Persians. Alexander the Great conquered Zabul during his conquest of Persia in the 320s BCE. The region later became part of the Seleucid Empire, which traded it to the Mauryan Empire in 305 BCE as part of an alliance. The Sunga Dynasty overthrew the Mauryans in 185 BC, but shortly afterwards lost Zabul to the Greco-Bactrian Kingdom. Zabul became part of the break-away Indo-Greek Kingdom in the mid 2nd century BCE.
Indo-Scythians expelled the Indo-Greeks by the mid 1st century BCE, but lost the region to the Parthians and Indo-Parthians in the early 1st century CE. The Kushan Empire soon expelled the Indo-Parthians and ruled Zabul until around 230 CE, when the Kushans were defeated by the Persian Sassanid Empire and were replaced by Sassanid vassals known as the Kushanshas or Indo-Sassanids. In 420 CE the Kushanshas were driven out of Afghanistan by the Chionites, who established the Kidarite Kingdom. The Kidarites were replaced in the 460s CE by the Hephthalites, who were defeated in 565 CE by a coalition of Persian and Turkish armies. Zabul became part of the surviving Kushano-Hephthalite Kingdoms of Kapisa, then Kabul, before coming under attack from the Moslem Arabs. Around 870 CE the Kushano-Hephthalites (aka Turkshahi Dynasty) was replaced by the Hindu-Shahi dynasty, which fell to the Ghaznavids in the early 11th century CE.
We are told that it was only in 870 AD that Zabulistan was finally conquered by one Yakub who was the virtual ruler of the neighbouring Iranian province of Siestan .The king was killed and his subjects were made Muslims