The only other entities Paine mentions in Common Sense (apart from the Brits, the Patriots, and the Pacifists) are the countries of continental Europe: mostly France and Spain. He mentions them because these countries might have some bearing on why America should or shouldn't go to war with Britain.
For example, Paine suggests that countries like France or Spain will never help America defeat Britain:
If we mean only to make us of that assistance for the purpose of repairing the breach, and strengthening the connection between Britain and America. (4.28)
Having a strong bond between America and Britain doesn't benefit these other countries in any way, so they're unlikely to help patch up US/British relations.
In addition to his earlier arguments, Thomas Paine insists that France and Spain might actually help Britain crush the American resistance if the Americans rebel. Or as Paine puts it:
While we profess ourselves the subjects of Britain, we must, in the eye of foreign nations, be considered as rebels. (4.29)
In other words, Spain and France would help Britain put down a rebellion in order to discourage this sort of thing from happening in their own countries. But if the Americans stand up and act as an independent country, Spain and France might help them win their independence just to stick it to the British.