Several people have asked about the foreign units that appear in the Operation Z trailer. This will be explained in detail later in the series and I promise it will make sense. The trailer featured a shot of South Korean Marines since they often train with US Forces and could probably slot in a joint force structure. There is also a shot of several Mirage fighter jets. In our back-story, these are Brazilian fighters contributing to the international aid force.
There is a much larger story we intend to tell in the future which focuses on what is happening in the rest of the world while America is focused on the outbreak.