What was a primary reason for the Northern opposition to Lincoln's Emancipation Proclamation?

The primary reason for the Northern opposition to Lincoln's Emancipation Proclamation stemmed from the desire for peace with the Confederate states. Many individuals in the North, particularly those who were not abolitionists, were concerned that the proclamation could prolong the Civil War by alienating Southern citizens and making reconciliation more difficult. They feared that turning the war into a fight against slavery would intensify Southern resistance and hinder efforts to reach a peace agreement. This perspective was particularly prevalent among Democrats and other groups who prioritized an end to hostilities over social reform.

While there were certainly other factors contributing to Northern opposition, such as concerns regarding military policies and civil rights advancements, the overarching concern about maintaining the Union and achieving a swift peace was a significant driver of the opposition to the Emancipation Proclamation.