 Complete the following phrase:  On 1 January 1956 Anglo-Egyptian Sudan declared independence as the Republic of Sudan; Chad followed later on 11 August 1960 and the border then became an international frontier between two independent states. Since then relations between the two states have often been tense, with each accusing the other of harbouring rebel groups which are allowed to cross the boundary. For instance, Sudan offered the FROLINAT rebel group sanctuary in western Sudan during the 