In the pre-industrial era, Derbyshire was a flourishing agricultural county, but it was one of the English counties most dramatically affected by industrialisation in the 18th and early 19th centuries, becoming noted in particular for the manufacture of heavy machinery and (during the Napoleonic Wars) of armaments. Its population grew swiftly (having reached 237,170 by 1831); but the electorate has been estimated at only 3,000 or 4,000 in the second half of the 18th century, and was probably not much higher by the time of the Reform Act. The Dukes of Devonshire were able to maintain much of their traditional influence, Cavendish members occupying one of the two seats as a Whig MP; but the county itself was predominantly Tory, and usually ensured that the other MP was returned in that interest.