The Confederacy? The interest seems to be the act of slavery and the war Lincoln is talking about must be the Civil War, which was taking place while Lincoln was addressing his second inaugural. Lincoln was reasoning that the Confederacy was fighting to keep slavery, which is the interest the "insurgents" have. Lincoln also did not want slavery to continue to spread, but he was fine with having slavery, "restrict the territorial enlargement if [slavery]".
Anvil is a tool used by blacksmiths, and it is the surface on which the object is placed which is worked on with a hammer- stroked with a hammer.
von Bülow meant (in 1899) that Germany will either have to colonize others ( be the hammer) or it would have to risk being colonized itself (being the anvil), hence showing the need for Germany to participate in colonization.
I believe it's B. Economics policies. During his presidency, he put forth a lot of economic policies.
