Socialism in the 20th century had its origins in Marxism.
Socialism applies to various ideologies/movements who believe that society should have a high degree of public, collective, or co-operative ownership. Such highly socialist societies range from societies where the government is almost the only owner of property (such as "dictatorship of the proletariat" communist states) to social anarchism. Societies having a high degree of socialism typically lack a capitalist and/or free market system but may have "market socialism" that includes price controls. A supposed characteristic of high degree socialist societies is the absence of a distinction between employers and the employed.
Even in capitalist societies is possible to create collectives and co-operatives as such societies are considered to be free societies. Early socialists sometimes thought that capitalist societies could be changed to socialist ones by an increasing number of such voluntarily collectivist organizations. However, such collectivist organizations have usually been out-competed by privately owned organizations. Critics of socialism argue that this demonstrates that collectivist organizations, at least in some circumstances, are less efficient than privately owned ones. Later socialists have often abandoned such attempts to voluntarily transition to socialism and instead in effect argued that socialism must be implemented through coercive and non-voluntary methods such as through Communist revolutions/coups.
Classifying an ideology or a society as socialist or not is sometimes difficult. Societies typically have both private and public ownership. Even classical liberal societies often include some publicly owned bodies and even Communist states often allow or allowed some private property. Several ideologies include the words "social" in their names (such as in "social liberalism") which may indicate support for a partially socialist society. It is possible to argue that some parts of the economy should be privately owned and argue that other parts (such as "natural monopolies") should be collectively owned.
Many socialists see their ideology as having arisen due to the poverty created by the industrial revolution (ignoring the agrarian poverty of previous centuries), and being largely responsible for rising living standards by forcing the rich to transfer part of their wealth to the poor due to measures such as higher wages forced by labour unions and due to higher taxes going into welfare systems. Critics of this have seen the scientific and technological revolutions as mainly responsible for increasing living standards. Classical liberals see wage competition between employers as being mainly responsible for increasing wages. That the industrial revolution even initially would have decreased living standards may be questioned. It may also be argued that while living standards for the new group of industrial workers in the cities initially were poor, their very survival and the large population growth would not have been possible without the agricultural revolution and that this survival of people who previously would have died should in itself should be seen as an improvement.
Pre-Marxist socialist or related views existed before the industrial revolution. It is possible to see early societies such as hunger-gatherers as highly socialist, ones with the whole societal group often working together in activities such as hunting and collectively sharing the gains. This may have caused an evolutionary inclination or sympathy towards socialism despite high degree socialism not necessarily working well in more complex societies. Some aspects of Christianity such as collectivist religious orders with the members not owning personal property may be seen as theoretically partly socialist.
Medieval societies have sometimes been seen as being more complex than the exclusively negative feudalism claimed by many socialist and liberal historians inspired by Marx. While not socialist (or liberal societies as a whole), European medieval societies have been seen as having a communitarian and integralist ideology in which society was seen as an organic unit with all parts and groups having responsibility towards one another (such as noblesse oblige and partly religiously based responsibilities towards the poor). Such more complex views have influenced some critics of socialism and liberalism (and many aspects of feudalism) such as some forms of conservatism, fascism (broad sense), and nationalism.