I figured out an interesting way to nuke units in mass. However this method nukes all the units of a team. Listen up and learn:
For the map that I have built, the city that needs to be defended by you, later launches a nuke off to some unknown place. It's mentioned in dialog as to what it could be. Doesn't matter really. But what does matter is, the enemy retaliates later on with permission from their country, to use nukes back in return. So the city gets blasted away. I figured what I could do is, for the challengemap, is to have all the units in the territory of the city, be a separate team that you control. When enemies come into the city, they change to another team as well, and anything you bring into the city, or leave from the city, will change team.
So what you need to do to work this:
You really need to have units that will change team. I did try by squad. That does work if the units in the squad were determined before the game started. I could not get the game to add units to a squad, it didn't work; not by area trigger. You can also have them change team by area trigger, like for my city. Entering the city changes it to a separate team, and leaving changes it back. Not the most ideal though, but it's better than nothing I guess. The next thing you need is a trigger. For me I went with a on turn change event, and compared a variable that would +1 each turn when it is told to start counting, and not until it is told. I went with a variable because I didn't want it counting until the player actually approaches the city and takes command to defend it. Before that I wanted it to be dormant. I then had another variable, this to be set to 1, and then after it's done killing units, set back to 0. I didn't want it deleting buildings that are captured, outside the nuke event. Next you gotta setup a trigger that removes units -1 of any team changed team, with a variable condition set to 1, to be turned back to 0 in a dialog or something. Try figuring your own way to disable the nuke on change team. The change team event trigger will be useful for when you tell the change round trigger, to change team of unit matching any type of unit of team "number here" to "number here".
Since I also am using trains in my map, I will need to figure out how carridges are handled when the train engine changes team. It would be great to say, if the engine here is taken, assume the carridges will change over along with the train. But a person may choose to leave the carridges behind unhooked. It would be great if the game handles this itself. Buuuut if it does not, then I will have to figure out something useful to counter a potential problem. I actually wonder if the train unhooks the carridges when the engine alone is changed team. What happens to the mechanics?