The First Atlantic War was a military conflict in the Maincanon between the Old Nations and the Commonwealth/New Frenco Empire, lasting from April 2129 to September 2132. It concluded with a status quo ante bellum between the Commonwealth and Old Nations, but is widely regarded as a prelude for the much larger-scale Second Atlantic War which occured several years afterwards.

The war began with an ON invasion of the Commonwealth's Scandinavian territory, and played out in three primary theaters: the ON conducted a large-scale (and relatively successful) submarine campaign in the North Atlantic ocean, a protracted air war played out over the British Isles and Northwest Europe, and heavy ground combat took place in Scandinavia itself.

Late in the war, military officers of the Old Nations forcibly deposed the government of Chancellor M.K. Lambert and replaced it with a provisional government, which quickly adopted a largely defensive strategic policy and prioritized a search for a peaceful resolution to the conflict. Two primary factors led to this series of events: the fact that the Old Nations' strategic situation was beginning to rapidly deteriorate, and the Mecharussian invasion of the Baltic Union, which had taken place several months prior.

Community content is available under CC-BY-SA unless otherwise noted.