Complex sentence: In the spring of 1941 Britain regained control of British Somaliland and conquered Italian Somaliland with the Ogaden, but until the summer of 1943 there was an Italian guerrilla war in all the areas of the former Italian East Africa.
Split into simpler sentences: In the spring of 1941, Britain regained control of British Somaliland and conquered Italian Somaliland with the Ogaden. However, until the summer of 1943, there was an Italian guerrilla war in all the areas of the former Italian East Africa.