In the years leading up to the Spanish American War, the United States experienced a growth in ethnocentrism, a belief in manifest destiny and Anglo-Saxonism. It was this combination of views that provided the moral impetus allowing for the U.S. public to support the efforts to make the country into an imperial power.
The law for slavery was enacted in 1850. The law was called T<span>he Fugitive </span>Slave Law<span> or Fugitive </span><span>Slave Act. Hope that helps. =)