Based on the illustration showing freed people with union army soldiers what assumption is the artist making about the effects

of the Emancipation proclamation

( ...) what assumption is the artist making about the effects of the Emancipation Proclamation? Former slaves would welcome the arrival of the Union army.

The Emancipation Proclamation was an executive order drafted/signed by Abraham Lincoln on January 1st, 1863, during the Civil War. Its purpose was to free the slaves in the South. The Union would still be a slave nation during the war, despite the fact that Abraham Lincoln would be laying the ground for a greater abolitionist movement. The Civil War was a rebellion that was currently underway in the south, with the North and the South divided due to ideological differences. With the South in a state of outright rebellion, it was on Abraham Lincoln's shoulder to try and preserve the Union at all costs.

The Union Army was the army that fought for the Union (North) during the American Civil War. It was comprised of several armies, to cover the many geographic regions in which the war was fought (the Union Army was victorious over the Confederate Army).