What foreign nation did William Seward suggest Lincoln instigate a war with to unify the US?

William Seward suggested that Lincoln instigate a war with Great Britain to unify the United States. He believed that a common enemy could rally the nation and distract from internal divisions. Seward's idea was rooted in the context of the Civil War, where he thought an external conflict could help solidify national identity. However, this suggestion was not pursued by Lincoln or his administration.