Lassalle avoided revolutionary activity for several years thereafter. He became a political commentator and wrote a short book on the war in Italy in which he warned Prussia against rushing to the aid of the Austrian Empire in its war with France. Lassalle followed this with a larger work on legal theory, published in two volumes in 1861 as "Das System der erworbenen Rechte" ("The System of Acquired Rights"). According to Bernstein, Lassalle wanted the book "to establish a legal and scientific principle which shall once for all determine under what circumstances, and how far laws may be retroactive without violating the idea of right itself"; that is, determining the circumstances under which laws may be made retroactive when they come into conflict with previously established laws.