For the first time in history, unmarried people head the majority of U.S. households. A total of 100 million adults, who make up 36-44 percent of the workforce, are single. Eighteen states and 300 cities now have unmarried majorities, and single people account for $1.6 trillionin annual consumer spending. Countries around the world are experiencing similar trends.

Single, a new documentary directed by Richard Atkinson and Jane Scandurra, takes a look at this major demographic shift. The film is equal parts insightful, objective, and entertaining. Since the average American will spend more time in his or her adult life single than married, it is surely a worthy topic for examination.

So why are so many Americans single? The film touches on several key factors.

One is the tremendous progress women have made in society: Many can support themselves outside of marriage. As Michelle Bernard shows in Women’s Progress, women are wealthier and healthier than ever before. Pick whatever measure you want, from education to income to workforce participation, and women are light years ahead of where they were even a few decades ago. Today, 22 percent of homebuyers are single women. That doesn’t mean women don’t want to get married, but it certainly relieves the economic pressure to do so.

Instead, people marry for love – funny as it may sound nowadays, love didn’t always rank very high on the “reasons to get married” list. But even marriage based on love isn’t all sunshine and lollipops. As sociologist Christine Whelan points out in the film, the emphasis on love creates huge pressure to meet the perfect mate, and many singles struggle with it. The good news, as Whelan points out in the film and in her book, Why Smart Men Marry Smart Women, is that today’s high-achieving women are getting married. They are just doing it later and having fewer children in the process.

Of course, the single trend is not without its downsides. In 2005, nearly 40 percent of kids are born out of wedlock. Some of that statistic appears to result from conscious choices: Many of the singles interviewed in the film said that if they weren’t married by a certain age, they wanted to have babies on their own.

Another issue, one that the film does not explore in detail, is the rise of extended adolescence. In recent years, researchers have found that people in their early twenties are less likely to think of themselves as adults. Relationships require compromise and the ability to put a partner’s needs first, both of which conflict with the “me” generation mentality.

The film also could have spent more time exploring the complicated landscape of relationships today’s young adults have to navigate. Relationships range from exclusive dating to casual dating to “friends with benefits” to “hooking up.” Further, sequence goes out the window: These are separate categories, and one does not necessarily follow from or lead to another.

offers valuable insights into a now-majority faction of American life. The shift isn’t necessarily a threat to marriage – after all, most people will eventually get married. But as one commenter points out in the film, “Marriage is no longer the only game in town.” If that’s the case, then we owe it to ourselves to understand the reasons why, and Single is a great starting point.

– Allison Kasic is director of the R. Gaull Silberman Center for Collegiate Studies at the Independent Women’s Forum.