Nigeria relatively little violence or voter fraud, in contrast to previous elections. In the March 2015 election, Muhammadu Buhari defeated Goodluck Jonathan by roughly 2 million votes. Observers generally praised the election as being fair. Jonathan was generally praised for conceding defeat and limiting the risk of unrest. Nigeria is a federal republic modelled after the United States, with executive power exercised by the President. It is influenced by the Westminster System model in the composition and management of the upper and lower houses of the bicameral legislature. The president presides as both head of state and head of the federal
Head of state heads of state, sometimes in addition to another title, such as the Ottoman Sultan. Historically, some theocratic Islamic states known as "imamates" have been led by imams as head of state, such as in what is now Oman, Yemen, and Saudi Arabia. In the Islamic Republic of Iran, the Supreme Leader, at present Ali Khamenei serves as head of state. The Aga Khans, a unique dynasty of temporal/religious leadership, leading the Nizari offshoot of Shia Islam in Central and South Asia, once ranking among British India's princely states, continue to the present day. In Hinduism, certain dynasties adopted a title