SDG16 (Promote just, peaceful, and inclusive societies) is a critical sustainable development goal without which all the other 16 sustainable development goals become inherently unsustainable. Justice, peace and inclusiveness are key ingredients for attaining the aspirations expressed in Agenda 2030 and its visions of a safe, prosperous and peaceful world. We used the problem tree analyses to x-ray the causes and consequences of conflicts, injustice and weak institutions, which are the negative outcomes of a not well implemented SDG16 and as a way to also underscore the criticality of issues under the purview of this SDG. The three problem tree analyses revealed that the causes/consequences of aggravated conflicts, injustice and weak institutions are often similar and interwoven. These three legs of peaceful coexistence, justice for all and strong enabling institutions are critical to ensure and enhance sustainable development at all levels. Any society with prevalent injustice cannot enjoy peace and societies need strong institutions to enforce justice. As can be deduced, strong institutions in active democracies can tame leadership impunity, allow for rule of law to thrive and assist in the controlling of the occurrence of crimes.