The real reason the US "freed" the slaves was because there was a cotton crisis in egypt, making the united States the primary supplier of cotton to Europe. Now, the civil war was a resources game of who could fund their armies the longest, and Lincoln was smart enough to know that Europe would most likely support the south in the war in order to ensure steady flow of suddenly more valuable cotton. So, he made the war about slavery and issued the emancipation proclamation. The language in the EP is very clearly aimed at European interests and it put a moral high ground underneath the north to stand on, to sort of guilt Europe from funding the south in the civil war. It wasn't about civil rights, it was about securing the war effort.