This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.
Q: London was the world's largest city from about 1831 to 1925. London's overcrowded conditions led to cholera epidemics, claiming 14,000 lives in 1848, and 6,000 in 1866. Rising traffic congestion led to the creation of the world's first local urban rail network. The Metropolitan Board of Works oversaw infrastructure expansion in the capital and some of the surrounding counties; it was abolished in 1889 when the London County Council was created out of those areas of the counties surrounding the capital. London was bombed by the Germans during the First World War while during the Second World War, the Blitz and other bombings by the German Luftwaffe, killed over 30,000 Londoners and destroyed large tracts of housing and other buildings across the city. Immediately after the war, the 1948 Summer Olympics were held at the original Wembley Stadium, at a time when London had barely recovered from the war.
A:
What was the primary cause of the cholera outbreak in 19th century London?