Did other countries support either side in the civil war?

Mainly it was Great Britain and France.

Recognition of the CSA by either would have made it difficult for the north to continue the war; by both would have virtually won the war for the south.

G.B. desired the cotton the south produced, but needed the food the north produced

But France wasn't going to do it without Britain, because it was embroiled in a foreign adventure in Mexico attempting to get a Habsburg prince enthroned as ruler.