What do young single women want? Sex, power, money, friendship, careers, clothes, husbands, babies – or none of the above? The short answer, according to All the Single Ladies: Unmarried Women and the Rise of an Independent Nation – a book American reviewers are falling over themselves to praise as a landmark account of singleness – is the freedom to shape their lives in ways they, society, and men, are only beginning to understand.

In a media blitz last week, New York author Rebecca Traister laid out her case: single women are a revolutionary force challenging social definitions, getting married later in life, or not at all, and changing “everything about the way the nation works”.

Not least politics: by making up nearly a quarter of the electorate, and leaning to the left of men and women in traditional marriages, single women are beginning to reshape the political sphere.

Her evidence: in the political realm, unmarried women made up 23% of the electorate and voted 2 to 1 for Obama over his Republican opponent, Mitt Romney, in 2012. Between 1890 and 1990, women were married, on average, at age 20 to 22. That number is now 27. Single adult women now outnumber married adult women in America.

Overall, 53% of adult American women are now single. Traister declares: “Huge numbers of women are saying: we are a changed nation and we require a different relationship with our government.” She told the online magazine Salon last week. “Independent women living outside marriage threaten all kinds of things about the way power is supposed to work.”

Rebecca Traister, catalyst for a media blitz last week. Photograph: Sarah Karnasiewicz

Traister, author of Big Girls Don’t Cry: the Election That Changed Everything for American Women in 2010, argues that singlehood is no longer as restrictive for women, and that all paths of life, including marriage, can be followed without formally attaching to a man. Leanne Shapton, a Canadian author who has looked at relationships through the artifacts couples collect, and last year published a book on women discussing their relationship to clothes, Women on Clothes, said she knew almost no one in a conventional marriage. “Female friendships are changing and becoming more interesting and possibly more sustaining the less they have to do with women talking about men or husbands.”

Kate Bolick, author of Spinster, cautions that we are in transition. “Women may have more advantages and opportunities than ever before, and can create their lives however they want them, but a lot of them are still carrying the ghosts of older ideas.”

Bolick wrote a story for the Atlantic in 2011 – also using Beyoncé’s call-out, All the Single Ladies – which looked at how the decline in men’s prospects was disrupting the romantic market, and with it, opportunities for traditional marriages. Yet even then, she says, being single was seen as a “loathsome condition”.

Five years on, the picture is quite different. Bolick says it’s not economic conditions that have changed but the numbers entering womanhood and setting forth. “The fact that women are coming of age with a rich conversation on this topic is exciting. It bodes well for individuals and society as a whole.” She adds: “Marriage is not going away. It’s just that people are staying single longer. In a world where everything is permissive, it puts the onus on women to figure out what they want. But we know marriage is not the right option for a lot of people.”

Meeting my husband and falling in love was an absolute shock Rebecca Traister

It has been 18 years since Sex and the City diverted feminist dialogue toward freedom through fashion and mate-selection. Traister is concerned with the other side of that coin: unmarried women who have been among the most successful writers, activists and thinkers – forerunners of the modern single woman. “Women,” she writes, “perhaps especially those who have lived untethered from the energy-sucking and identity-sapping institution of marriage in its older forms, have helped to drive the social progress of this country since its founding.”

In her own life, Traister spent “14 independent years” after university advancing her own life as a single woman and, ultimately, planned to have a baby on her own. She married five years ago at 35 and now has two children. She told the Tampa Bay Times her time as a single woman, and the importance of the female friendships she formed, set “the bar higher for marital relationships”. “You learn from them what intimacy can be. You gain a healthy expectation of how to support other people.”

The switch from sisterhood to marriage, she recalled, was painful. “I was used to being single, independent, on my own. Meeting my husband and falling in love was an absolute shock.” She quotes Charlotte Brontë, married at 38: “It is a solemn, strange and perilous thing for a woman to become a wife.”

Julie Anderson, a former model who now collates women’s stories about themselves, Feminine Collective: Raw & Unfiltered Vol 1, offers a slightly different interpretation of the change: “Women heard their mothers saying, well, if I hadn’t married your father so early I’d be doing this or going there. They taught their daughters that they don’t need a man for anything, not for validation or even for sex. They taught them to be about me, me, me, and they’re not going to have kids early because there’s so much they want to do.”

Still the culture wars grind on. Last week, rightwing talk radio host Rush Limbaugh called a Georgetown University law student a “slut” for her support of women’s access to birth control. The student, Sandra Fluke, said she considered Limbaugh’s comments “an attempt to silence me, to silence all of us”.

Not only does a gender pay gap persist – according to US government statistics, full-time female workers are paid 80.4 cents for every dollar earned by full-time working men – but men’s wages are growing at twice the rate of women.

There is a growing evidence that sufinancial equality is becoming a prerequisite to a relationship. The Federal Reserve Board last year published a study indicating that similar credit scores – or the qualities credit scores represent – play a significant role in whether people form and stay in relationships.

But despite persistent remaining inequalities, Traister believes young, single women are pushing the Democratic party to the left, in part through their support of Bernie Sanders. And Donald Trump may soon find a “new category of citizens”, who are finding the measure of their economic and political power.

Traister told the Observer young women could put their newfound power into action by voting and “simply continuing to live and earn and take up more space in the world”.

This would “force a reckoning with the fact that adults don’t live the way they used to any more”, she said in an email, “that adult life for women has been revolutionised and is unlikely ever to be organised around marriage as THE defining institution again.”