As a result of the acceptance of the Lord Lugard Amalgamation Report by the British Government, the Northern and Southern Provinces were joined together to form Nigeria on 1st January, 1914.
The principle of individual ministerial responsibility refers to the convention that a minister is responsible to every actions of their department / ministry and it's applicable in the presidential system of government. Collective responsibility is to cabinet or parliamentary system of government where ministers are collectively responsible for there decisions.