Basically Europe had other things going on/ didn't think the war mattered much to them since the U.S. wasn't really important at the time. Most officially stayed neutral or diplomatically supported the Union. Britain played both sides and was involved in suppling wartime materials, munitions and even some ships to the Confederacy to keep the cotton flowing. The confederacy planned on using Europe's dependency on its cotton as a tool to gain additional support, but early into the war there was a European cotton surplus and they found alternative sources. Also Europe was having bad farming years and Northern grain was valued more over the southern cotton.

Along with the cotton surplus, both Britain and France had abolished slavery. When President Lincoln issued the Emancipation Proclamation, it made the war about slavery. Neither side wanted to be internationally known for supporting slavery after abolishing it themselves, so they back off.