WARSAW, Poland – Zygmunt Bauman, one of the most prominent and prolific European sociologists of recent decades, has died at 91. The Polish-born left-wing thinker’s works explored the fluidity of identity in the modern world, the Holocaust, consumerism and globalization.

Bauman died at his home in Leeds, England, on Monday surrounded by his family, according to Anna Zejdler-Janiszewska, a Warsaw-based philosophy professor and friend of Bauman’s.

Renowned for an approach that incorporated philosophy and other disciplines, Bauman was a strong moral voice for the poor and dispossessed in a world upended by globalization. Whether he was writing about the Holocaust or globalization, his focus remained on how humans can create a dignified life through ethical decisions.

He wrote more than 50 books, notably “Modernity and the Holocaust,” a 1989 release in which he differed with many other thinkers who saw the Holocaust as a breakdown in modernity. Bauman viewed the mass exterminations of Jews as the outcome of such pillars of modernity as industrialization and rationalized bureaucracy.

In the 1990s, Bauman coined the term “liquid modernity” to describe a contemporary world in such flux that individuals are left rootless and bereft of any predictable frames of reference.

“In a liquid modern life there are no permanent bonds, and any that we take up for a time must be tied loosely so that they can be untied again, as quickly and as effortlessly as possible, when circumstances change,” Bauman wrote.

In informing friends in Poland of his death Monday, Bauman’s wife wrote that he had gone “to liquid eternity.”

Beyond Poland, Bauman’s theories were a major influence on the anti-globalization movement. He focused on the outcasts and the marginalized, describing how many people have seen their chances of a dignified life destroyed by the new borderless world.

“The key thing was that Bauman did not talk at or down to his audience – when he was talking he was listening, when he was teaching he was learning. His books and seminars were places where we could come together and explore together how to be human,” Keith Tester, co-author of “Conversations with Zygmunt Bauman” and a former student of Bauman’s, told the Associated Press on Monday.

Bauman was born Nov. 19, 1925, in Poznan, Poland, into a Polish-Jewish family that had suffered poverty and anti-Semitism, something that inspired his lifelong belief in tolerance and social justice. Speaking decades later of how he became a communist, he recalled his family’s poverty, the “blows and kicks” inflicted on him by non-Jewish children on the playground and “the humiliations which my father, a man of impeccable honesty, had to suffer from his bosses to feed his family.”

He was not yet 14 when Germany invaded Poland in September 1939 and World War II began. His family survived the Holocaust by fleeing to the Soviet Union. There, Bauman, still a teenager, joined a Polish army unit that was formed under Soviet command, earning Poland’s Military Cross of Valor for his bravery.