We offer a novel decomposition of wealth inequality and quantify principal factors determining changes in US wealth inequality. We show that the rise in inequality reflects mainly demographic factors related to rising life expectancy and associated increases in savings -- it is not per se evidence of growing inequity and a ”threat to society”. Importantly, the rise in inequality has been largely driven by differences between rather than within birth cohorts, a phenomenon that has gone largely unnoticed in the literature. Moreover, while changes in saving behavior mitigate the rise in wealth inequality, demographic factors increasingly amplify it. We discuss implications for policy and for structural modeling.