Complex sentence: By the 18th century canvassing was standard practice, but this was also an era of gross electoral corruption, and canvassing was used to bribe and threaten voters, as famously depicted in William Hogarth's "Humours of an Election" series of paintings.
Split into simpler sentences: By the 18th century canvassing was standard practice, but this was also an era of gross electoral corruption, and canvassing was often so associated. Canvassing was also frequently used to bribe and threaten voters, as famously depicted in William Hogarth's "Humours of an Election" series of paintings.