Paralleling the evolution of Chinese and Indian cultural traditions was the movement toward a distinctive monotheistic religious tradition in the Middle East, which found expression in Persian Zoroastrianism and in Judaism. Neither of these religions themselves spread very widely, but the monotheism that they nurtured became the basis for both Christianity and Islam, which have shaped so much of world history over the past 2,000 years. Amid the proliferation of gods and spirits that had long characterized religious life throughout the ancient world, monotheism—the idea of a single supreme deity, the sole source of all life and being—was a radical cultural innovation. That conception created the possibility of a universal religion, open to all of humankind, but it could also mean an exclusive and intolerant faith.