Complex sentence: The Emancipation Proclamation outraged white Southerners (and their sympathizers) who envisioned a race war, angered some Northern Democrats, energized anti-slavery forces, and undermined forces in Europe that wanted to intervene to help the Confederacy.
Split into simpler sentences: The Emancipation Proclamation outraged white Southerners (and their sympathizers) who envisioned a race war. It angered some Northern Democrats, energized anti-slavery forces, and undermined elements in Europe that wanted to intervene to help the Confederacy.