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POD: Sometime during the war UK gets very unlucky or makes an unfortunate mistake and loses both carriers. (notably one of them was set to be decommissioned) Argentina capitalizes on this and gains a formidable advantage in the region. Continuing a conventional war will be very difficult and costly in lives and money.

The UK is capable of making bombing runs from St Helena as they demonstrated earlier in the war. Do they threaten nuclear war? Do they go ahead and nuke a military target, or a large city? I'd guess they wouldn't target Beunos Aires because of the proximity to other countries. If they drop one or more nukes Argentina will almost certainly surrender unconditionally. What would the international response be?
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