Answer:
The effect of British Colonial was that on the one hand it changed the Traditions and Political Structures within the Area called Nigeria forever, on the other it dragged a feudal area into the 20th Century.
Prior to the British entering into Nigeria, Amelioration was comman place and encouraged. Slavery was rife. Especially in the north under the Muslim states. Another major problem was that modern education was non existent. While the Muslim states were relative advanced in their education and political systems these were limited in terms of bring about a Nation state the size of modern Nigeria. On the other Hand theYoruba civilization was at an exhausted phase having under when a number of major wars especially against the Fulani. This was undermining the Power in Ife Ife,
The British brought generally peace and provided a relatively feudal mass modern facilities in terms of Education in the West & East, not so in the North as Sir Fredrick Lugards promise to the Sultan of Sokoto was upheld and minial Western influence was imported up north to the Hausa and Fulani states, this was to cause major problems when Nigeria was to be forced to be independent in the 1960's, and resulted in the British rigging the Elections in favour of the North, under the fear that the Southern Nigerian States would subsume it's Northern counterpart.
The rigging of the Elections and the Cameroon Mandate and split with Nigeria, embolderned the Igbo's to seeks like wise and separate causing the Biafrian War which ironically ended up Uniting Nigeria rather than dividing it.
The British brought Nigeria into direct contact with the Global Market Place for it's products as during it's brief 60 years of Colonial History, Nigeria was generally self sufficient. it was run by less than 2,000 British Colonial officers who relied on the co-operations of the existing Traditional Leaders. This was known as In Direct rule a system developed by Sir Fredrick Lugard and expounded upon by Mr Cameron in the 1920's\30's after the Aba Womens Riots. This policy had the dual effect of moderating Traditional leaders powers yet retaining them. However once Britain became bankrupt after the Second World War and was forced by the Americans to give up it's Empire in return for Loans and a more pivitol role in Europe. The nascent self governing political parties that Britain encouraged sought to undermine the Traditional Leaders and brand them as "Colaborators" of the old regime. This allowed young and Western Educated Polical Leaders like Zik or Awolo (spelling!) to ursup the Traditional Leaders by taking advantage of the Zeitgeist namely the handing over of Soveriegnty back to the Nigerian Peoples by the British.
British Colonialism installed in Nigeria the foundations of a Modern, if not troubled democracy, with Parlimental Institutions, Legal Institutions Education, the Christain Missionary School ( CMS) played a great part in reducing Africian supertitious beliefs that hindered alot of progress.