Natural borders – Physical features such as lakes, mountains or rivers can separate countries. Often, natural borders are the most successful borders between states because of their inarguable division.
eg Us and mexico - river grande
political intervention - Borders are drafted by the sovereign state, and may have been influenced by past empire expansion.
eg scramble for africa - 14 countries met in berlin in 1884-5 to discuss how to divide up africa
Rwanda - where clashing ethnic groups within one state spiralled into the genocide of 800,000 Tutsis.