Totalitarianism offered no room for independent institutions, or for rival systems of belief. The Catholic church was both. It came under agonising pressure, infiltrated, intimidated, and its clergy labelled as foreign stooges, peddlers of superstition, crooks and reactionaries. Some believers switched sides, joining "progressive" pro-regime front organisations. Others went underground. For the first time in centuries, martyrdom became a real choice for believers, in the heartlands of Christian Europe.

Before his arrest, Cardinal József Mindszenty of Hungary issued a statement absolving in advance Catholics who might be forced to sign documents denouncing him. Torture forced a garbled confession, in which he admitted participation in a plot to restore the Habsburgs, steal the crown jewels and start a third world war.

His counterpart in Poland after 1948, Cardinal Stefan Wyszyński, took a less antagonistic approach, hoping to buy time for the church to recover from the devastation of the war. Controversially, he signed an agreement with the authorities in 1950, instructing clergy to foster respect for the law — in effect abandoning the underground resistance. It did not stop him being arrested too. 

Applebaum's book is so persuasive that it is easy to overlook how controversial it is. She explodes in particular the notion that the Soviets tightened their grip on their part of Europe in response to ill-judged bellicosity from Western warmongers. Like Gulag, her previous masterwork, Iron Curtain will make uncomfortable reading for soft-headed apologists for the failed Soviet experiment, and for those who see the Soviet system only as a phoney threat used to justify McCarthyism and hysterical anti-Communism. 

It also explains in a manner worthy of Arthur Koestler what totalitarianism really means. In the final chapters of the book she details the Soviet system's relentless desire to hunt down every fragment of independent life and thought. Freemasons, for example, had deep historical roots in Hungary. But the notion of a secret society, even one based on altruism and reason, was impermissible. Education, and anything that would influence young people, was a priority for the Communists too. That meant rewriting children's stories to make them ideologically correct. University admissions were skewed to encourage workers and discourage the bourgeois-in a way that for some British readers may have unpleasant echoes of the modern fashion for "fair access".