An estimated one-quarter of the world currently lives without electricity. Liberia, among others, is fighting to change this: after the second of two civil wars in the last 25 years ended in 2003, the country's electrical grid had been destroyed. President Ellen Johnson Sirleaf was elected in 2006 in part on a platform to return widespread electricity to the country, and she has recently claimed that, by 2015, 30 percent of the country's urban population and 15 percent of its rural population will be restored to the national grid. Craig Koslofsky is author of "Evening's Empire: A History of the Night in Early Modern Europe," explains how electricity has historically changed politics, culture, and society.