Complex sentence: Harrison, though several years out of active politics was a war hero with roots in both North and South, and as he had been fired by Jackson, looked attractive as a possible presidential candidate to the new party, something that Harrison did nothing to discourage.
Split into simpler sentences: Harrison, though several years out of active politics was a war hero with roots in both North and South, and had been fired by Jackson. Thus, he looked attractive as a possible presidential candidate to the new party, something that Harrison did nothing to discourage.