A protest song is often a kind of folk music, but in recent times protest songs come from all genres of music, including punk rock and hip hop. Such songs become popular during times of social disruption and among social groups and their supporters. They protest perceived problems in society: injustice, racial discrimination, war, globalization, inflation, social inequalities and the like.
Folk songs occur throughout history, as in the American Revolutionary War and in the abolitionist movement of the 1800s. In the 20th century, the union movement, the Great Depression and the Vietnam War also spawned protest songs. Some protest music traditions also date back to the American Civil War, when traditional songs such as 'We Shall Overcome' served as protest songs.
A common form of folk protest song, often with acoustic guitar and harmonica, was popularized by the work of Woody Guthrie and Pete Seeger in the beginning of the 20th Century. This tradition was continued into the middle of the century by Phil Ochs and Bob Dylan. Many protest songs were based on the Vietnam war and recently, the war in Iraq.
For examples of many different types of protest songs, see List of protest songs.