There's a timeline thread in the works but all you or anyone else really needs to know is that in 2023, a resistance movement in C107 (a city in the former American Rust Belt) sparked a wider rebellion when it destroyed Granite Peak (North American Nova Prospekt), precipitating the fall of dozens of Combine cities and the destruction of the Spire network (which held the North American Exclusion Zone i.e. The Zone but Xenian, at bay). Consequently, the NAEZ is expanding at a rapid rate, necessitating the gradual evacuation of the North American continent. The server takes place some time later in 2024.