Engels wrote this book between late 1842 and early 1845. While still in his very early 20s, he had already written extensively as a journalist for both English and German newspapers. At the time, England was undergoing significant political and economic changes - the Chartist movement was pushing, inter alia, for universal suffrage and the country was just coming out of a deep slump in economic activity, which had lasted from 1837 to 1842. Meanwhile the country was undergoing a massive wave of industrialisation that would see it soon become "the workshop of the world". Engels had moved to Manchester at the behest of his father to learn to be a businessman and Engels used the opportunity to write a report for his fellow radicals in Germany on the state of the working class given the massive upheavals taking place - a sort of prior warning what to expect should industrialisation take place in Germany - the original was published in German and an English version would only be released in 1886 for an American audience.
Engels vividly describes the working and living conditions of the working class predominantly, although not only, in Manchester, and links this to the economic developments taking place. This is based on researching Factories Inspectors reports - a method that was to be copied by Marx in Volume 1 of "Capital" and contemporary newspaper articles as well as his own eyewitness reports garnered by walking around the affected areas and interviewing locals. It is a very professional and accomplished work of investigative social reporting, and no less than UNESCO has included it on its list of most influential works of sociology.
There is no 'call to arms' here in this book - this is still to wait until "The Communist Manifesto" in 1848 but there are shades of "A specter is haunting Europe" particularly in the final chapter.
Marx was to compliment Engels long after for its passion and incisiveness. It is a classic of its times.