He spent a year in England, and then went back to Africa. He had determined now to explore certain districts to the northeast of the great lakes. They were in the hinterland of British East Africa, and England had a vague claim over them; but no actual occupation had taken place, and they formed a series of independent states under Arab emirs. He went this time with a roving commission from the government, and authority to make treaties with the local chieftains. Spending six years in these districts, he made a methodical survey of the country, and was able to prepare valuable maps. He collected an immense amount of scientific material. He studied the manners and customs of the inhabitants, and made careful observations on the political state. He found the whole land distracted with incessant warfare, and broad tracts of country, fertile and apt for the occupation of white men, given over to desolation. It was then that he realised the curse of slave-raiding, the abolition of which was to become the great object of his future activity. His strength was small, and, anxious not to arouse at once the enmity of the Arab slavers, he had to use much diplomacy in order to establish himself in the country. He knew himself to be an object of intense suspicion, and he could not trust even the petty rulers who were bound to him by ties of gratitude and friendship. For some time the sultan of the most powerful state kept him in a condition bordering on captivity, and at one period his life was for a year in the greatest danger. He never knew from day to day whether he would see the setting of the sun. The Arab, though he treated him with honour, would not let him go; and, at last, Alec, seizing an opportunity when the sultan was engaged in battle with a brother who sought to usurp his sovereignty, fled for his life, abandoning his property, and saving only his notes, his specimens, and his guns. When MacKenzie reached England, he laid before the Foreign Office the result of his studies. He pointed out the state of anarchy to which the constant slave-raiding had reduced this wealthy country, and implored those in authority, not only for the sake of humanity, but for the prestige of the country, to send an expedition which should stamp out the murderous traffic. He offered to accompany this in any capacity; and, so long as he had the chance of assisting in a righteous war, agreed to serve under any leader they chose. His knowledge of the country and his influence over its inhabitants were indispensable. He guaranteed that, if they gave him a certain number of guns with three British officers, the whole affair could be settled in a year.