Why can't nuclear tests affect international waters? As you progress in the nuclear tests it becomes a challenge in itself to find a place to carry it out, it cannot take districts, forcing the player to loot them, it also cannot affect luxury or strategic resources, ok, and it needs to be completely in national territory, so far ok, it would not make sense to be able to do this in foreign soil.

But with irregular territories, finding an area of radius 4 that does not affect any resources is difficult enough, but as it is not allowed to reach territories of international waters, which can never be claimed, it is almost impossible to find a nuclear test site that does not require destroy an entire city, affecting about 3 territories.

For me, the most interesting places for this type of event, as well as space launches, are small islands, as it is not possible to take full advantage of their territorial extension. However, they are often isolated by territories of open sea, international waters, and so one of their few uses literally goes down the drain. A strange fact, since in practice most of the known nuclear tests were carried out on islands in the Pacific or in desert regions. Ideally, the nuclear tests need to be positioned in national territory, but their fire area can reach international waters, that is, tiles that can never be claimed.