The episode reinforces the show’s recurring theme of moral ambiguity: "Are there any good guys?". Clarke’s decision to bring weapons and Diana’s choice to sacrifice the Ark for her own survival both stem from a perceived need for protection, yet both actions result in catastrophe. The 100 episode 9 review: Unity Day | Den of Geek

"Unity Day," the ninth episode of The 100 ’s debut season, serves as a masterclass in narrative irony. While the title commemorates the historical unification of the 12 international space stations to form the Ark, the events that unfold both in orbit and on the ground depict a brutal shattering of any remaining cohesion. The episode explores the tragic gap between the ideal of peace and the harsh reality of survival-driven paranoia.

The disunity is even more literal on the Ark. While Chancellor Jaha attempts to foster a sense of shared purpose through the Unity Day celebration, a treacherous faction led by Diana Sydney carries out a violent coup. A bomb intended for the leadership instead kills innocent civilians, including Marcus Kane’s mother.