The free world, to put it succinctly, is a land of mass incarceration as well; how it got to this point, a question examined in an excellent Netflix documentary named “13th,” is likely to surprise many – and perhaps to upset many, once the conversation around it begins to erroneously center on which party to blame. Though Democrats and Republicans are deeply divided on various subjects, it is often forgotten how many times they have concurred in their policies. Director Ava DuVernay (“Selma”) explores one significant instance in her second documentary, probing into the war on crime and the strengthening of it by figures on both major sides. The work is neither a liberal smear campaign on conservative policies nor vice versa; it is systematic in its approach and leaves a considerable impression.

One reason for this is the placement of a modern-day issue within an historical context. Despite the film’s focus on mass incarceration, it becomes clear early on that the documentary intends more than to address simply the present, as the opening 10 minutes are a primer on racism in the South throughout the late 19th and early 20th centuries. The remainder of the documentary then unfolds in chronological order, from the Nixon administration to the early 2010s. This, while occasionally resulting in speedy coverage of time periods, is a largely effective method. Because of such an approach, viewers are first and foremost reminded of how ubiquitous racism once was and what it was responsible for when it was; this enables a greater emotional effect when race-related problems of the far nearer past are discussed, and the chronological form of this discussion gives the documentary coherence.

Additionally, DuVernay’s filmmaking has strengthened since “Selma.” The history of African-Americans in the United States is recalled in a well-crafted array of interviews, news excerpts and archival footage. The editing of the interviews gives the film a consistent pace. Historical videos are sometimes used to make effective and disturbing parallels.Impressively, “13th” makes a case that is more common among liberals while avoiding strong partisanship in its tone and presentation of events (which a fair number of persuasive works fail to do). The fomenting of the prison-industrial complex is its central focus, and this sets viewers up for a closing sequence that ranks as one of the most stirring endings of its decade, one which was clearly meant to provoke thought and which will succeed in this goal for many years. The director said in an interview that the documentary’s credit sequence “is about black joy, because black trauma is not our life.” Her film is frequently bleak, but remains loyal to the above statement: It can in many ways be considered a lamentation, but is not so much of one as to make viewers fatalistic. It is at once an important historical document and a critical call to action.