Corporate Wars
The Corporate Wars is a turbulent period running from about 2060 forward, marked by paramilitary "proxy wars" fought between private security firms and mercenaries working for the Megacorporations rather than official state actors. The causes, outcomes, and methods of these wars varied considerably throughout the entire time period, ranging from resource squabbles through to, effectively, "marketing", where one Megacorporation would attack another to demonstrate their attitudes toward (e.g.) citizen freedoms, such as in the Hong Kong Meltdown of 2064.
The time period was also marked by frequent conflicts between Megacorporation security forces and various rebel groups, such as governmental loyalists, Chain Breakers, or the Disconnected. For the most part, the United Nations stood by and allowed these conflicts to take place as they were clearly pursued by non-state actors. The one exception to this was that United Nations Counter-NBC Task Force troops were frequently deployed into hot zones to ensure the wars were fought by "conventional" means.