Why was the Civil War considered the first modern war?

How many citizens of mexico does it take to equal the ecological footprint of the average citizen of the united states? it takes nearly three mexican citizens to equal the ecological footprint of the average u.s. citizen. it takes about 12 mexican citizens to equal the ecological footprint of the average u.s. citizen. it takes just over eight mexican citizens to equal the ecological footprint of the average u.s. citizen. two citizens of mexico equal the ecological footprint of one average citizen of the united states. they are essentially equal?

What directive in source a might have been at the root of the action described in source b?

What would lead a historian to consider two events to have a relationship of correlation rather than causation?