Final answer:
Abraham Lincoln's primary diplomatic goal was to preserve the Union and prevent international recognition of the Confederacy, relying on both political maneuverings to maintain support and the Emancipation Proclamation as a means to weaken Confederate resources and discourage foreign support.
Step-by-step explanation:
Abraham Lincoln's main diplomatic aim was to preserve the Union and prevent international recognition of the Confederacy. Lincoln sought to calm southern fears while simultaneously mobilizing Unionists to stand behind his policies, indicating his intention to maintain federal law on all Union property without resorting to violence, unless necessary. He repudiated secession, upheld the inviolable nature of the Union, and emphasized the significance of majority rule.
Additionally, Lincoln's Emancipation Proclamation and the Union army's victories disrupted the southern slave labor system, making abolition a condition for rebelling states upon their return to the Union. Moreover, incorporating emancipation into the Union cause also served as a diplomatic tool to discourage British support for the Confederacy, aligning with anti-slavery sentiments in Britain.