They are all independent,
here is a list of the series.
Soldiers: Heroes of WWII (2004) - single player campaign and multiplayer/co-op
Silent Heroes (2006) - single player campaign only
Faces of War (2006) - single player campaign and multiplayer/co-op
Men of War (2009) - single player campaign and multiplayer/co-op
Men of War: Red Tide (2009) - single player campaign only
Men of War: Assault Squad (2011) - multiplayer/co-op skirmish
Upcoming
Men of War Vietnam (2011) - single player campaign and co-op multiplayer only
Hope that help.