Burnham's seminal work, The Managerial Revolution (1941), theorized about the future of world capitalism based upon its development in the interwar period. Burnham begins by saying that "It is a historical law, with no apparent exceptions so far known, that all social and economic groups of any size strive to improve their relative position with respect to power and privilege in society". He then weighed three possibilities: (1) that capitalism was a permanent form of social and economic organization and would continue indefinitely; (2) that it was temporary and destined by its nature to collapse and be replaced by socialism; (3) that it was currently being transformed into some non-socialist future form of society. Since capitalism had a more or less definite beginning in the 14th century, it could not be regarded as an immutable and permanent form. Moreover, in the last years of previous economic systems such as those of Ancient Greece and the Roman Empire, mass unemployment was "a symptom that a given type of social organization is just about finished." The worldwide mass unemployment of the depression era thus indicated that capitalism was itself "not going to continue much longer."