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1st implemented by the English in Ireland over a 1000 years ago
I'm no expert on this particular period, but this is a stretch. It was only around this time that England began to exist as a politically unified kingdom. The invasion of Ireland that occurred not long after was initiated by the Normans, who at the time ruled England having invaded from Northern France, and were the descendents of Vikings, and so on...
The problem post independence is that whatever European power had control would use a divide and rule 1st implemented by the English in Ireland over a 1000 years ago and then rolled out all over the world. The issue between ethnic groups in Africa is that all sharing space formed along European borders