Extermination through labour (or "extermination through work", Vernichtung durch Arbeit) is a term that was adopted to describe forced labor in Nazi concentration camps in light of the high mortality rate and poor conditions; in some camps a majority of prisoners died within a few months. In the 21st century, research has questioned whether there was a general policy of extermination through labor in the Nazi concentration camp system because of widely varying conditions between camps. German historian Jens-Christian Wagner argues that the camp system involved the exploitation of forced labor of some prisoners and the systematic murder of others, especially Jews, with only limited overlap between these two groups. Some writers, notably Aleksandr Solzhenitsyn, have written that the Soviet Gulag system was also a form of extermination through labour. Similar statements have been made about the Laogai system under Mao Zedong's China. The term "extermination through labour" (Vernichtung durch Arbeit) was not generally used by the Nazi SS. However, it was specifically employed by Joseph Goebbels and Otto Georg Thierack in late 1942 negotiations involving them, Albert Bormann, and Heinrich Himmler, relating to the transfer of prisoners to concentration camps. The phrase was used again during the post-war Nuremberg trials. In the 1980s and 1990s, historians began debating the appropriate use of the term. Falk Pingel believed the phrase should not be applied to all Nazi prisoners, while Hermann Kaienburg and Miroslav Kárný believed "extermination through labour" was a consistent goal of the SS. More recently, Jens-Christian Wagner has also argued that not all Nazi prisoners were targeted with annihilation. Wagner states, "As a metaphor for moral indignation, the use of the term ‘annihilation through labour’ by historians may be completely understandable; but it is not particularly helpful in an analytical sense, since it implies an ideological programme and, in doing so, disregards the impetus of contingent factors which emerged in the course of the war.