Why Do We Need a One History?

I'm interested in the broad sweep of why important things happen and how they develop over time. I want to know why sovereign states emerged in the late Middle Ages, why the Roman Empire's political system crumbled. But throughout this series, I'm still going to be telling stories about what it would have been like to have lived through these massive social and political changes. These were people who worked and had children, loved and hated, lived and died in the shifting currents of history.