An article on Slate makes the distinction between polyamory and extreme forms of polygamy by noting the "surprisingly woman-friendly" origins of modern polyamory.
Author Libby Copeland traces polyamory's roots to the Victorian era, when some women began expressing discontentment with monogamy and traditional gender roles. The piece then discusses a commune in New York where 300 people practiced what they called "complex marriage" from the 1840s through the 1870s. Next came bohemians, beatniks, and hippies who fought back against conventional marriage, and fringe groups in the 1970s which practiced group marriages.
Then there was the 1990s through today:
During the '90s, the Internet sparked a third wave of polyamory, after AIDS had driven it underground during the '80s. A Usenet newsgroup called alt.polyamory helped build a community, and a woman calling herself Morning Glory Zell, member of a "neo-Pagan" organization called the Church of All Worlds, helped popularize the term in an article called "A Bouquet of Lovers." In more recent years, polyamory has mainstreamed somewhat, becoming fodder for features in Newsweek and on ABC's Nightline. MTV did a True Life documentary on polyamorous young people, books like The Ethical Slut explored the topic, and Dan Savage continues to champion non-monogamy.
. . . Women are in many ways the driving force behind polyamory as a movement these days, having been integral in founding its organizations and documenting its history . . . the first books on the movement were written by women . . . a sizable number of polyamorous households consist of more men than women, the opposite of how polygamy typically expresses itself.
Read the rest on Slate.