Opponents of the mexican war. such as henry david thoreau and abraham lincoln, thought: a. manifest destiny extended north toward canada, not south toward the rio grande and mexico b. it was an unjust and unfair war in which a stronger nation was beating up on a weaker nation c. mexico was too big and powerful and that a war with it would cost too many lives and be too expensive d. the united states had grown enough and didn't need to fight mexico for more land.