After 1600 the area was united under one ruler and began trading and making connection with Portuguese traders and members of the military through the Mozambican port which was occupied by Portuguese. By 1700 the empire had broken up into areas that were controlled by individual groups of people which was known by the Portuguese by collecting information. The Swahili-Arab slave trade had its highest amount in the middle of 1800s when about 20,000 people were forced to become slaves and were sold every year.