Anti-Judaism is the "total or partial opposition to Judaism — and to Jews as adherents of it — by persons who accept a competing system of beliefs and practices and consider certain genuine Judaic beliefs and practices as inferior."
Anti-Judaism, as a rejection of a particular way of thinking about God, is distinct from antisemitism, which is more akin to a form of racism. Scholars wishing to blur the line between theology and racism have since coined the term religious antisemitism.
Nevertheless, the concept of Judaism has been challenged over the past two thousand years by scholars of both Christendom and Islam.
In Ancient Rome, religion was an integral part of the civil government (see Religion in ancient Rome). Some Emperors were proclaimed gods on Earth, and demanded to be worshiped accordingly throughout the Roman Empire. This created religious difficulties for monotheistic Jews and worshipers of Mithras, Sabazius and Early Christians. Jews were prohibited by their biblical commandments from worshiping any other god than that of the Torah (see Shema, God in Judaism, Idolatry in Judaism).
The Crisis under Caligula (37-41) has been proposed as the "first open break between Rome and the Jews", even though problems were already evident during the Census of Quirinius in 6 and under Sejanus (before 31).