Here are several reason why the bid for international support failed:
-Bumper cotton crop in 1860 gave a surplus of cotton
-When an 1862 cotton shortage occurred Europeans find their supply replacement elsewhere, like in Egypt or India
-Brisk trade between Union and Britain with the american grain and flour helped offset the decline of textiles industry and encouraged neutrality
-Union military successes makes French and British feel discouraged to ally with struggling confederacy in order to avoid loss
-Lincoln said an alliance with Confederacy was an alliance with slavery and the Europeans were already anti slavery way before the Americans
-Unions cause linked freedom with democracy