Q:I know that the answer to the question "Which is further south, the steppes or the Islamic heartland?" is in "The Kushan Empire, a collection of Yuezhi tribes, took control of the region in the first century CE and ruled until the 4th century CE during which time Buddhism, Nestorian Christianity, Zoroastrianism, and Manichaeism were all practiced in the region. Later the Hephthalite Empire, a collection of nomadic tribes, moved into the region and Arabs brought Islam in the early eighth century. Central Asia continued in its role as a commercial crossroads, linking China, the steppes to the north, and the Islamic heartland.". Can you tell me what it is?
A:
Islamic heartland