WFM membership declined sharply from 1911 to 1916. In part, this was due to the continuing intense opposition from mine owners in the West. But conflict with the IWW also led to significant membership losses. Historian Vernon H. Jensen has asserted that the IWW had a "rule or ruin" policy, under which it attempted to wreck local unions which it could not control. From 1908 to 1921, Jensen and others have written, the IWW attempted to win power in WFM locals which had once formed the federation's backbone. When it could not do so, IWW agitators undermined WFM locals, which caused the national union to shed nearly half its membership. Paul Brissenden noted WFM dissatisfaction with the IWW in Jerome, Arizona in 1913, attributing some of the friction to the fact that the WFM was becoming more conservative, accepting contracts with employers and affiliating with the AFL, while the IWW was becoming more revolutionary. (The IWW would not begin to accept contracts with employers until 1938.)