Complex sentence: In 1921, at Atlantic City, he placed clear second in the Eighth American Chess Congress; this series of nine tournaments, staged at irregular intervals between 1857 and 1923, was the forerunner to the modern United States Chess Championship tournament series.
Split into simpler sentences: In 1921, at Atlantic City, he placed clear second in the Eighth American Chess Congress. This series of nine tournaments, staged at irregular intervals between 1857 and 1923, was the forerunner to the modern United States Chess Championship tournament series.