Democracy and human rights
According to the White House's report on "The Economic Benefits of U.S. Trade" just released "López-Córdova and Meissner (2005) is among the best studies trying to estimate a link from trade openness to democracy. Following the long literature estimating the link between trade and income (discussed earlier), the authors employ a gravity model specification to obtain instruments for international trade openness, using information dating back to 1870. Their work reports a positive impact of trade openness on democratization."
You can find the full report here.