Massive changes have taken place in the way nations and nationalism are thought about. From being viewed enthusiastically by historians as a force for beneficial change before the First World War, today appeals to 'national' sentiment are viewed as far more complex and problematic. This book looks at how historians (and others, such as sociologists and political theorists) have explained the development, and enduring importance, of national identities from c.1850 to the present day. It compares and contrasts a wide range of different theories, and will be useful for anyone wanting to equip themselves with a theoretical understanding of why we live in nations, and why we invest them with such significance.