Women's liberation movement
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The Women's Liberation Movement was a feminist political movement which developed in the 1960s and 1970s, and was one important strand in Second-Wave Feminism
The term 'women's liberation' was coined in the early 1960s, when the word liberation was becoming popular, but (for example) the first Women's Liberation Conference in Britain took place in 1970, at Ruskin College. Publications such as Spare Rib and off our backs were founded in the 1970s.
It generated mythology almost before it was born such as bra burning - and it was a matter of deep concern to those within it at the time that its history would be rewritten by those who weren't in it. One important reality was that it is more sensibly seen as a movement of the 1970s and 1980s, not the 1960s, despite often being described as a 1960s phenomenon.
Second Wave Feminism 
There was always a creative tension between a growing general climate of liberalisation - culminating in legal liberalisation in the late 1960s and early 1970s, for example on abortion, gay rights and equal pay in the UK; what was termed a 'second wave' of liberalising feminism, perhaps best characterised by the formation of the National Organization of Women (NOW) and the Equal Rights Amendment (ERA) in the USA; and a more 'liberation' inspired movement with strong roots in the US Civil Rights Movement - and, it must be said, as much reacting against as working with the more radical political groups of the late 1960s.
To see the blossoming of the latter, it is most useful to look at publications coming out of 'the underground', such as off our backs in 1970 in the USA (still strong today) and Spare Rib in 1972 the UK. It could be argued that Spare Rib itself did not explicitly identify itself as part of the women's liberation movement until its coverage of the 2007 National Women's Liberation Movement Conference - before that still working out how much it aimed to be a challenging popular women's magazine and how much an explicitly radical political publication. (See the Penguin Spare Rib Reader for a good description and depiction of its development.) The fact that Spare Rib reached its high point of circulation and influence (after some very good PR when it first started) in the late 1970s usefully charts the women's liberation movement itself.
It's in 1981, for example, the European Union invited editors from the four leading WLM magazines in Europe (from Germany, France, Italy and UK) to a debate on women's rights in the European Parliament in Luxembourg; and the number of women's initiatives in the late 1970s has still to be documented. It is important not to back date views and influence: the 1970s were a crucial time for significant changes in attitudes to women in Western societies.
Some argue that the Women's Liberation Movement was a consequence of World War II, during which so many women got to experience "men's" jobs. This gave them a taste of the working life and the drive to fight for equality in society in the years to come, so they could continue to expand the traditionally "female" roles, as they were known then.
The 1980s 
The WLM ran into problems in the 1980s, both with a political backlash more generally, and questions about which women it was speaking for. It had always had extremely vociferous critics, from the tabloid press to Marxist groups; and, generally, not a happy relationship with the so-called 'stars' of feminism such as Betty Friedan, Gloria Steinem or Germaine Greer. The WLM didn't much agree with 'stars' or leaders (although Simone de Beauvoir was certainly honoured by many within it). After years of being defined as loony women's libbers, it found itself attacked as elitist and racist.
For the record 
The WLM also had an interesting relationship with academic women's - and then 'gender' - studies. The history and analysis of feminism in the 1970s and 80s is now mostly done by academic researchers, who may or may not have experienced it, or fully grasped what provoked and propelled women to organize within it.
One source for the earliest days of the more radically feminist roots of the WLM is Alice Echols, Daring to Be BAD: Radical Feminism in America 1967 - 1975 (1989). She describes the first explicit 'women's liberation' groups forming in 1968 in the USA. It makes little sense to talk about the WLM existing in any form before then.
An important reference for the more radical impulses of the WLM later on is the Trouble and Strife Reader, published in 2010, and its Introduction on both the magazine and its political context from 1983 to 2002.
A good more general history of the WLM has yet to be written. Several groups attempted at the time to capture history from its living actors; and the Feminist Library in London as well as the University of Wisconsin at Madison (which had a tireless feminist librarian in the 1970s and 80s) are good sources for original material.