In this nuke games refer to sanction cards.
25% reduced income for 20 turns or 100% reduced income for 999 turns.
Generally you would only have one card the whole game, maybe have the option to gain another every 25 turns.
They can be set up with everyone gets a nation bonus much like a diplomacy game, but either have diplomacy rule or remove the rule to declare war much like a free for all, but played with caution.
Here are some variants:https://www.warlight.net/MultiPlayer?TemplateID=887998
What i want from you is your opinion on different types of settings/maps/rules etc that you think works best.
I chosen the 25% for 20 turns one to played as a diplo where a superpower is aggressive, and the idea was to make players work together.