The grunt rebellion was the 29th age of conflict. It started because the grunt population pushed the Yig Yar out of their territory, and in turn the Yig Yar put infertility drugs in their recreational drug that I forget the name of. This escalated to conflict when the covenant refused to take notice. It was eventually put down by the elites, who in their tradition, forgave them. Afterwards the grunts were allowed to carry weapons, when before they hadn't.