I conclude that this proclamation is not an outright abolition of slavery, even though it settled liberation of slaves in the Southern states. It provided the chance to all slaves who would be able to flee from Southern states to get their freedom and, if they wanted, to enroll in the army. Lincoln didn't say that all slaves will be free, but only "all persons held as slaves within said designated States and parts of States". Obviously, it was a war measure, and not a civil rights act.
The linking verb, otherwise known as the copula verb, is was. Assassinated is the main verb, while was is the linking one.
