In 331 BC, Alexander the Great of Macedon began one of the greatest conquests in human history. After conquering Egypt and defeating the Persian Empire Alexander had pushed his army to the very limits of the world as the Greeks knew it. But he wanted more; he saw that the world extended further. By conquering the ancient lands of the Mesopotamians, he came into contact with cultures to the east, such as Pakistan and India. After almost a millenium and a half, from the period of Harappa (2500-1750 BC), to the end of the Brahmanic period, the peoples of India entered into no commerce or trade with the Mesopotamians. But starting around 700 BC, the Indians began to trade again with the Mesopotamian cities, and by the time of Alexander, that trade was dyanmic. Partly out of curiosity, and partly out of a desire to conquer the enitre world within the boundaries of the river Ocean (the Greeks believed that a great river, called Ocean, encircled all the land of the world), Alexander and his army pushed east, through northern Iran and all the way to Pakistan and India. He had conquered Bactria at the foot of the western Himalayas, gained a huge Bactrian army, and married a Bactrian princess, Roxane. But when he tried to push on past Pakistan, his army grew tired, and he abandoned the eastward conquest in 327 BC.

   Alexander only made it as far as the region of Gandhara, the plain which lies directly west of the Indus River. Alexander himself seems to have had literally no effect on Indian history, for he left as soon as he reached the Indus. Two important results, however, arose because of Alexander's conquests: first, from this point onwards Greek and Indian culture would intermix. But most importantly, the conquest of Alexander may have set the stage for the first great conqueror of Indian history, Chandragupta Maurya (reigned 321-297 BC), who, shortly after Alexander left, united all the kingdoms of northern India into a single empire.