Complex sentence: Granger was not a candidate for reelection in 1842, but was member of the peace convention of 1861 held in Washington, D.C. in an effort to devise means to prevent the impending war.
Split into simpler sentences: Granger was not a candidate for reelection in 1842. He was then a member of the peace convention of 1861 held in Washington, D.C. in an effort to devise means to prevent the impending war.