Complex sentence: By the mid- 1950s he was working for the "Daily Mirror", where his Andy Capp cartoon had its debut in 1957, making its way to the United States in 1963.
Split into simpler sentences: By the mid- 1950s, he was working for the "Daily Mirror", where his "Andy Capp" cartoon strip had its debut in 1957. It made its way to the United States in 1963.