Why Did Lincoln Write The Emancipation Proclamation

Why would Abraham Lincoln write the Emancipation Proclamation to free some of the slaves but not all of them? When I think about it, I can come up with three different reasons why Lincoln would want to write up a Proclamation that freed some slaves, the first reason, and probably the most obvious reason was because Lincoln wanted these people to be free, even if that meant he could not free everyone, it was at least a start. The following reason why I think that Lincoln wrote the Emancipation was because slaves were such a big presence in the South's Army, and allowing the slaves to come over to the otherside were everything was nicer, and they were free would entice lost of slaves to leave and as a result cripple the Southern Army. The final reason that I can conclude that it helped the Union make friends with the other countries, because at that time most of the other countries were

I think that he did realise that there might be a chain reaction from outside countries but I do not think that that was the main purpose of writing it. Many people may even challenge why he wrote it but in reality he had every right to write it as the president of the United States. Even without people questioning his authority, many people may question why he just freed the Slaves in the Confederacy, and I think that it was mainly because the target goal from a Military perspective was to deny the Confederacy recognition by England and France where slavery was illegal. However Lincoln's main goal was to free most of the slaves, however I do not think that this really made that far because who in their right mind from the South is going to share with the slaves that the Union is offering a free ticket into their regions for freedom. When they had all these workers helping fight for them, and do their work for