Complex sentence: It became a rallying cry for Northerners in the events that would later be termed Bleeding Kansas, and the political fallout was a significant setback for the Pierce Administration, effectively ending any possibility of Cuba's annexation until after the American Civil War.
Split into simpler sentences: It became a rallying cry for Northerners in the events that would later be termed Bleeding Kansas. The Pierce Administration suffered a significant setback, effectively ending any possibility of Cuba's annexation until after the American Civil War.