In the modern age, some parts of the world are experiencing a long peace. Nuclear weapons, capitalism and the widespread adoption of democratic institutions have been credited with fostering this relatively peaceful period. Yet, these accounts overlook one of the most dramatic transformations of the 20th century: the massive redistribution of political power as millions of women around the world won the right to vote.

Through gripping history and careful reasoning, this book examines how the political influence of women at the ballot box has shaped war and peace. What would a world ruled by women look like? For more than a hundred years, conventional wisdom held that women's votes had little effect. That view is changing - it turns out that women voters had a profound effect on the world we know and in ways we hardly understand. A world ruled by women's voices is a world that is less willing to fall in love with war as a noble end in itself, less prone to lapse into violence for the sake of maintaining an image. In other words, it is the world we live in now, more so than we have ever realized.