It also took a while to notice the effects of cigarette smoking.

While tobacco was used by Europeans in some quantity since the early colonization of North America, it was the mass-production of cigarettes in the late 19th century that made heavy smoking a possibility for a large number of people. The first medical work showing a link between smoking and cancer came out in 1912 and 1929.

But smoking didn't get really huge in the U.S. until the mid-20th century, the era of mass media marketing of cigarettes (L.S./M.F.T.!); the British Doctors Study in 1956 was statistically pretty darned conclusive from a Bayesian standpoint, but was famously opposed by R. A. Fisher. Much of the later controversy on the subject of tobacco and cancer was manufactured by the tobacco industry, well after the matter was scientifically settled.

Sources:
http://en.wikipedia.org/wiki/Health_effects_of_tobacco_smoking
http://www.cdc.gov/tobacco/data_statistics/tables/economics/consumption/
http://en.wikipedia.org/wiki/British_Doctors_Study