In the late 1800's, the world faced both the threat of unfettered capitalism as demonstrated by the 'Robber Barons' who had built monopolies in various markets, and the socialist/communists who spread the ideas of collectivism and governmental control.
Pope Leo XIII jumped in with what many consider the first encyclical of modern Catholic Social Theology, Rerum Novarum.
A follow-up post will discuss the Pope's insights on capitalism, but his document starts with a condemnation of socialism. He lays out three key criteria for consideration:
1) The right to private property
"If (the socialist plans to take private property) were carried into effect the working man himself would be among the first to suffer."
"Every man has by nature the right to possess property as his own."
2) The eminence of the individual and family over the state
"Man precedes the State, and possesses, prior to the formation of any State, the right of providing for the substance of his body."
"The contention, then, that the civil government should at its options intrude into and exercise intimate control over the family and the household is a great and pernicious error."
3) The affect of socialist programs with the sin of covetousness
"The door would be thrown open to envy, to mutual invective, and to discord, the sources of wealth themselves would run dry...and that ideal equality about which they entertain pleasant dreams would be in reality the leveling down of all to a like condition of misery and degradation."
"divine law...forbidding us in severest terms even to cover that which is another's"