There's a distinct parallel between the Spartans and the Tenno.
ONI purposefully forged the Spartans - first to quell the Insurrection and later, to combat the Covenant. The Orokin, through their experiments with Void jumps, inadvertently created the Tenno and then forced them to fight a war.
The UNSC didn't believe they could maintain intergalactic integrity without the Spartans. The Orokin believed they would not have survived without the Tenno. The UNSC taught the Spartans to be unfalteringly loyal, raising a small army on Reach. The Orokin similarly manipulated the Tenno, training them so that they could later deploy them against the Sentients.
In either case, humanity and agency were sacrificed in the name of order and security. In either case, children were made soldiers and sent to the front lines. There's a grey-morality parallel there - the idea that, to some, the ends justify the means, and that desperate times call for desperate measures, right and wrong be damned.
