Haile Selassie attempted to modernize the country through a series of political and social reforms, including the introduction of Ethiopia's first written constitution and the abolition of slavery. He led the failed efforts to defend Ethiopia during the Second Italo-Ethiopian War and spent the period of Italian occupation in exile in England. He returned to lead Ethiopia in 1941 after the British Empire defeated the Italian occupiers in the East African campaign. He dissolved the Federation of Ethiopia and Eritrea, which was established by the UN General Assembly in 1950, and integrated Eritrea as a province of Ethiopia while fighting to prevent their secession.