Most people will die from a lack of clean water, and other sanitary water related issues. Then everything else.
If it is a CME of significant level, everyone will be in the same situation regardless of border. The Sun does not pick sides, and the duration could cover the whole globe.
EMP, there could be collateral damage.
If a EMP was only aimed at the US, I dont think anyone will be trying to invade. 350million people all losing their minds and the military will be at DEFCON 1/NORAD. Better to take advantage of the situation, while the US trys to deal with the domestic issues, China takes Taiwan back, Russia makes moves where they want, the Mid-East is anyones guess, and I would not rule out North Korea taking advantage of the situation either.