Border clashes and rows about oil wealth cloud the relationship between South Sudan and Sudan eight months after the south seceded, with some fearing a new outbreak of open warfare.

One man with a rare insight into the two countries is photographer Tim McKulka. He spent five years travelling to every state in the united Sudan - then Africa's biggest country - to produce a book We'll Make Our Homes Here: Sudan at the Referendum, which will soon be available for free on iTunes.