Originally, the breakaway movements started as disquiet against the Colonial Administration Authority's oversight of the Outer Colonies, with the colonists tired of the organization's often overbearing bureaucracy. It first started as peaceful protests, and after years of frustrating negotiations, some groups began to use more forceful methods, eventually abandoning diplomacy in favor of terrorist tactics.
Initially confined to a few systems, the fighting spread across human-controlled space in only several years; as the conflict escalated further, even some Inner Colonies, as inwards as the Epsilon Eridani system and the Sol system, were targeted by rebel militants and terrorists. What had once been widespread support for the Insurrectionists quickly dried up at the outbreak of violence. Though they started out targeting only military and Colonial Administration targets, as the UNSC counterinsurgency operations began more and more innocent people were caught in the crossfire.
The Insurrection claimed millions of lives between the late 2490's and the mid-2520's. The various rebel groups had become extremely adept at creating improvised explosive devices difficult for the UNSC to detect, and therefore stop, and had struck many high profile targets, even in orbit above Reach itself. Some opponents of the war believed the simplest solution was to simply give the rebels their autonomy - for the UNSC to pull out, and let the rebels have their independence. However, the value of the colonies made them simply too important to abandon, as it would bankrupt the Inner Colonies.
The Insurrection died down almost instantly after the onset of the Human-Covenant War that began in 2525. However, isolated insurgent groups staged operations against the UNSC throughout the war, whittling down humanity's precious resources from the war effort against the alien hegemony. By 2540, all but one of the Insurrectionist groups that continued their hostilities against the UNSC abandoned their efforts, when the genocidal goals of the Covenant were made public knowledge. After the end of the war in 2553, some of the surviving Insurrectionist groups—as well as all-new ones—proceeded to resume their fight against Earth, leading to a resurgence of the conflict after the war. This time, however, much of the focus was on the general populace's anger at the UNSC's alliance with the Sangheili, a race whom had just months prior slaughtered billions. Many called for massive reparations to be put upon the Sangheili for their crimes, of which only a fraction were paid due to the generosity and personal guilt of Thel 'Vadam. One group, the Fist of Man, began covert and sporadic terrorist operations against both the UNSC and civilians on worlds such as Balaho, Sangheilios, and Eayn. The Insurrection remained active at the time of the Guardians' emergence across human space on October 28, 2558.