Atheism is the lack of belief in any deities. Marxists, and the communist movement generally, have historically embraced atheism. Religious variants of communism and socialism do exist however, such as Islamic socialism and Christian communism. Jesus, on the other hand, is often characterized as implicitly socialist. Opposition to religion was based on abuse by church leaders of their power over believers to oppose efforts by the people to govern themselves as well as on the church's emphasis on the rewards of the after-life rather than on struggle against the troubles of this life.
The alliance of the church with the rulers, at least in the Christian world, dates to the adoption of Christianity by the Roman Empire and establishment of Christianity as the State church of the Roman Empire Wp→, which is to say the church of the rulers, a practice which was universally followed in Christendom throughout most of its history.