Socialism is an economic system which is characterized by common ownership and management of the means of production by workers. However, this can take many forms, such as public, collective or cooperative ownership.
The initial goal of socialism is to lead to a communist state, as stated by Marx and Marxist authors. This was because many problems of modernity were attributed to capitalism. However, socialism has evolved and is now adopted by several countries in a mild form. Socialism changed because of the pressure of reconciling this idea with ingrained elements of our government, such as democracy, capitalism and efficiency.
The most important reason for socialism to evolve was the difficulty in dismantling capitalism. Not only is capitalism engrained in our society (so much so that eliminating it would cause enormous disruption), but people appreciate many things that capitalism brings, such as innovation, competition, the possibility to amass great fortunes, etc.
A second reason that led to the split of socialism is the fact that democracies in the West tend to be very strong. Politicians need to respond to the demands of constituents, and many Americans associate socialism to negative outcomes, due to Cold War propaganda. Although support for socialism has increased in recent years, it is still not widely accepted. Support in Europe is higher, although still limited.
Finally, there is a growing attempt to adopt some of the benefits of socialism without having to change the economic system completely. This is known as social democracy, and for many countries, it is a blend that allows them to enjoy the best of both worlds. Although this blend has led to mostly positive outcomes, it has also led to the weakening of traditional socialist ideology.