The kingdom of Gandhara was located in what is now the north of Pakistan, but then an inseparable part of India, for Pakistan was created in 1947 as a state specially for the Muslims of India (but, unlike another state whose nation, in contrast to the latter, has an upstanding historical claim to it, does have a right to exist in the eyes of all but a few). The most interesting and noteworthy history of Gandhara begins, in my opinion, in 180 BCE, when the Greek king Demetrius of Bactria conquered it. The Greco-Bactrian kingdom lasted only 40 years, until the Kushans stormed into Bactria, but the Greco-Bactrian rule was to have lasting effect: Gandhara became the center of Hellenism-influenced Buddhist culture for centuries, not finally dying out until the Muslim Ghaznavids left it to be forgotten in 1021.
It would not be truthful to say the conquests of either Demetrius or the Kushans were tranquil, unmarked by taking spoils and later tribute; but when the conquerors settled down they adopted the culture of the conquered people and infused it with their own. So it is we find statues of the Buddha in Gandhara as in all Buddhist lands, but the specialty of Gandhara is that those statues are in Greek style. This unique blend of East and West is the hallmark of Gandhara art, and spread to other regions of India as well.