Complex sentence: In spite of opposition, science fiction in comics continued in the U.S. through the 1960s with stories for children and teenagers, and began to return to the adult market again in the late 1960s with the wave of hippy underground comics.
Split into simpler sentences: In spite of opposition, science fiction in comics continued in the U.S. through the 1960s with stories for children and teenagers. It began to return to the adult market again in the late 1960s with the wave of hippy underground comics.