Marx: Dead or Alive?

Why did so many socialist theories of economics emerge in Europe in the mid 19th Century, and why do you think those of Karl Marx grew to be more influential than the others? Why do you think capitalism has continued to flourish despite Marx's claim that it is destined to fail? Do you believe that there will be new social-economic theories emerging if capitalism encounters troubles, and if so what might these be? Please post a thoughful response by Friday 3/1/12.