The really weird thing about the Emancipation Proclamation, according to what I've read, is that it freed slaves only in the Confederate states which were taking up arms against the Union but not the slaves in Union territory (and there were some slaves and slave owners in Union territory at that time). Thus it was an adroit political move by Lincoln, essentially strictly a propaganda move as it could obviously not be enforced upon the South at that time. It potentially threatened only the interests of the Confederacy while serving as a marvelous propaganda device to help persuade England and France not to support the Confederacy...as slavery was very much looked down upon in England and France. England and France had both been leaning toward supporting the Confederacy, as they would have preferred to see the USA split permanently into 2 weaker powers, but once Lincoln had "freed the slaves" it was no longer really possible for England and France to openly side with the Confederacy, as it would not have been politically acceptable to their general population.

The War Between the States was not being fought to free the slaves in its earlier phase. It was being fought to restore the Union, and all Lincoln's rhetoric had indicated that...until he issued the Emancipation Proclamation. At that point the war became transformed into a moral crusade to free the slaves...and this was an idea that resonated far better with both the Union population (who were angry about conscription) and the European powers than a more prosaic struggle to simply "restore the Union" (which the English and French public certainly couldn't care less about...).

It's been dressed up in far more idealistic terms since...sanitized, you might say, for modern consumption, but Lincoln did not go to war to free the slaves, he went to war to end secession and restore the Union.

In a separate matter...people also tend to forget that (some of) the defenders of the Alamo were slave owners, while the Mexican government which fought them had outlawed slavery some time previously.

There's usually more to the picture than is found in the popular eye.