It didn't benefit European nations, it handcuffed them. Tom was using a different meaning of "benefit." The EP tied abolition, as a goal of war, to the Union and, by extension, tied slavery to the Confederacy. The people of Britain (for example) were none too fond of slavery, so direct support for the Confederacy was no longer an option.
The black soldiers in the Union army were free before the EP, so it didn't free them. Slave-holding states in the Union, such as Missouri, Maryland, and Kentucky, were unaffected by the EP. The EP was more a statement of intentions than anything else.