Following the wave of democratization during the 1990s, elections are now common in low-income societies. However, these elections are frequently flawed. We investigate the Nigerian general election of 2007, which is to date the largest election held in Africa and one seriously marred by violence. We designed and conducted a nationwide field experiment based on randomized anti-violence grassroots campaigning. We find direct effects on violence outcomes from exploring both subject-surveying and independent data sources. Crucially, we establish that voter intimidation is effective in reducing voter turnout, and that the violence was systematically dissociated from incumbents. We suggest that incumbents have a comparative advantage in alternative strategies, vote buying and ballot fraud. Voter intimidation may be a strategy of the weak analogous to terrorism.