The history of anarchy goes back to prehistory, when humans arguably lived in anarchic societies long before the establishment of formal states, realms or empires. With the rise of organised hierarchical bodies, scepticism toward authority also rose, but it was not until the 19th century that a self-conscious political movement emerged. During the latter half of the 19th and the first decades of the 20th century, the anarchist movement flourished in most parts of the world and had a significant role in workers' struggles for emancipation. Various anarchist schools of thought formed during this period. Anarchists have taken part in several revolutions, most notably in the Spanish Civil War, whose end marked the end of the classical era of anarchism. In the last decades of the 20th and into the 21st century, the anarchist movement has been resurgent once more.