In the final installment of the series, the broadcaster ends his chronicle of civilisation by bringing the story into the 20th century, when he believes humankind was propelled forward by technological brilliance but limited by the consequences of political failings, best demonstrated by the two world wars. Marr also touches on the more positive achievements in the fields of science and technology, as people now live longer and travel faster than their ancestors could ever have imagined, then speculates on what the future holds for a planet of seven billion people and rising.