Great Britain and France
There would be a great amount of peace for all nations at that time.
So that it could not be captured by the north.
If you mean who they fought against than that would be the Confederates.
Britain decided the test of Confederate viability would be whether Lee succeeded in his invasion of the North in September 1862. When this failed, Lincoln felt confident enough to issue the Emancipation Proclamation. After that, free nations abroad could not aid the Confederates without looking pro-slavery themselves.
The immediate and flash-point for the beginning of WW1 was the assassination of Archduke Francis Ferdinand who was the heir to the throne of the Austro-Hungarian empire. Secondly, the intricate web of European alliances with nations prepared to go to war, became the second cause of WW1. The alliances were complex and the willingness of the European powers to begin a war that would become the largest war in history to that time.
Northers would fight a long time
hgftud
They felt that dictators would lead their nations to war against their neighbors.
It would entangle the United States too deeply in the foreign affairs of European nations.
During the Civil War, the south sought help from European nations, especially Great Britain. They asked for support with men, weapons, etc. They though the plan would work because it was quite equivalent to the American Revolution, but European nations ultimately denied any support.
China?
By making it impossible for free nations abroad to help the Confederates without looking pro-slavery themselves.
At the Berlin Conference of 1884-1885 the European nations decided on how they would divide up the ownership of Central Africa to avoid fighting over it. The conference didn't actually approve the territorial claims of the European nations, but they did agree on a set of rules to avoid conflict in partitioning of the region.
They felt the United Nations lacked the power to enforce its decisions.
neutrality prolamation
Free nations abroad could no longer support the Confederates without looking pro-slavery themselves.
The effects of a russian invasion on Ukraine would be negative economic on Eastern European nations.