Sassou Nguesso was an opposition leader for five years before returning to power during the Second Republic of the Congo Civil War, in which his rebel forces ousted President Pascal Lissouba. Following a transitional period, he won the 2002 presidential election, which involved low opposition participation; he was re-elected in the 2009 presidential election. The introduction of a new constitution, passed by referendum in 2015, enabled Sassou Nguesso to stand for another term. He was re-elected in the 2016 presidential election with a majority in the first round.