English was imported to many parts of the world during the days of British colonial rule and along with it came the convention of referring to historical dates using B.C and A.D during the colonial and post-colonial periods. This convention slowly percolated to history books in every part of the world. It replaced Pre-colonial conventions for referring to historical dates that anchored around other historical personalities in other traditions of the world. For example, the anchor years for a non-English native would be 579 A.D for the Muslims, 544 B.C for Buddhists and 2105 B.C for the Hindus. But having a common era reference across all nations is essential in the internet age.
BBC has directed that the traditional B.C. (Before Christ) and A.D. (Anno Domini, or Year of the Lord) be replaced by B.C.E. (Before Common Era) and C.E. (Common Era) in its television and radio broadcasts. This has incensed British Christians. You can read the full article by clicking this link The convention of referring to historical date references using B.C/A.D is a result of wide spread acceptance of English as a common language among nations. Now BBC is broadcast in many nations and BBC website caters to folk speaking many languages from many cultures