Tens of thousands of colonists entered Morocco. Some bought up large amounts of the rich agricultural land, others organised the exploitation and modernisation of mines and harbours. Interest groups that formed among these elements continually pressured France to increase its control over Morocco a control which was also made necessary by the continuous wars among Moroccan tribes, part of which had taken sides with the French since the beginning of the conquest. Governor general, Marshall Hubert Lyautey, sincerely admired Moroccan culture and succeeded in imposing a joint Moroccan-French administration, while creating a modern school system. Several divisions of Moroccan soldiers (Goumiers or regular troops and officers) served in the French army in both World War I and World War II, and in the Spanish Nationalist Army in the Spanish Civil War and after ("Regulares"). The institution of slavery was abolished in 1925.