The idea is that according to the trailer and press release, "Motherland: Fort Salem" is set in an alternate version of America where witches have agreed to fight for the United States in exchange for an end to their persecution. The series follows three young women from basic training in combat magic into terrifying and thrilling early deployment. In this world, the traditional roles of gender and power are flipped with women on the front lines to fight looming and terrorist threats that are strikingly familiar to our world, but with supernatural tactics and weapons..."
The intro title also provides some interesting clues as the nature of the timeline, including a map of the United States: