A Short History of Violent State Atheism
Atheism is a great idea. In some places and at some times in its history, this great idea came into power as a state ideology. In such cases, and not unlike some other great ideas before it like monotheism, state atheism often motivated campaigns to try and eradicate the competition (i.e. all religions) through banning, murder, torture, detention, psychiatric treatment or other forms of violence to religious officials and discrimination toward believers. Below are the most radical cases.
This is not to say that atheism or atheists are bad, just that obviously, religion holds no monopoly on violence.
Albania
State atheism in Albania was taken to an extreme during the totalitarian regime installed after World War II, when religions, identified as imports foreign to Albanian culture, were banned altogether.[25] The Agrarian Reform Law of August 1945 nationalized most property of religious institutions, including the estates of mosques, monasteries, orders, and dioceses. Many clergy and believers were tried, tortured, and executed. All foreign Roman Catholic priests, monks, and nuns were expelled in 1946.
China
During the Cultural Revolution, student vigilantes known as Red Guards converted religious buildings for secular use or destroyed them.
Cuba
Originally more tolerant of religion, Cuba began arresting many believers and shutting down religious schools after the Bay of Pigs invasion, its prisons since the 1960s being filled with clergy.[48] In 1961 The Cuban government confiscated Catholic schools, including the Jesuit school Fidel Castro had attended. In 1965 it exiled two hundred priests.[49]
The Communist Party of Cuba defines one of its aims as "the gradual overcoming of religious beliefs by materialistic scientific propaganda and the cultural advancement of the workers."
France
The de-Christianization of France during the French Revolution is a conventional description of the results of a number of separate policies, conducted by various governments of France between the start of the French Revolution in 1789 and the Concordat of 1801, forming the basis of the later and less radical Laïcité movement. The goal of the campaign was the destruction of Catholic religious practice and of the religion itself.
Under threat of death, imprisonment, military conscription, and loss of income, about twenty thousand constitutional priests were forced to abdicate and hand over their letters of ordination, and six thousand to nine thousand of them were coerced to marry. [ this being France after all

]
By the end of the decade, approximately thirty thousand priests had been forced to leave France, and others who did not leave were executed. Any non-juring priest faced the guillotine or deportation to French Guiana. By Easter 1794, few of France's forty thousand churches remained open; many had been closed, sold, destroyed, or converted to other uses.
USSR
State atheism in the Soviet Union (gosateizm) attempted to stop the spread of religious beliefs as well as remove "prerevolutionary remnants".
Within about a year of the revolution, the state expropriated all church property, including the churches themselves, and in the period from 1922 to 1926, 28 Russian Orthodox bishops and more than 1,200 priests were killed (a much greater number was subjected to persecution). Most seminaries were closed, and publication of religious writing was banned. The Russian Orthodox Church, which had 54,000 parishes before World War I, was reduced to 500 by 1940.
Although all religions were persecuted, the regime's efforts to eradicate religion, however, varied over the years with respect to particular religions, and were affected by higher state interests. Official policies and practices not only varied with time, but also in their application from one nationality and one religion to another. Nationality and religion were always closely linked, and the attitude toward religion varied from a total ban on some religions to official support of others.
Adapted from:
http://en.m.wikipedia.org/wiki/State_atheism