In all the cultures where Islam has become ascendant, the Muslim authorities have attempted to rewrite the history of the conquered lands to obliterate the memory of anything that went before Islam. By this method the cultural contribution of civilizations that preceded Islam — during jahiliyah, “the days of ignorance” — is minimized, denigrated, and distorted.
The destruction of physical evidence is part of the revisionist task. To the average Western scholar, the Bamiyan Buddhas and the archeological artifacts buried in the ancient rubble under the Temple Mount are priceless treasures which must be preserved, restored, studied, and admired. But to a Muslim they are abominations and must be destroyed. If not actual idolatry, they are evidence of non-Muslim civilizations that preceded the introduction of Islam, and are thus an affront to the pride of the entire Ummah.
It has recently been discovered that an exiled Iranian academic literally took a scalpel to valuable Persian history books in the British Library and the Bodleian Library, removing inconvenient and offensive text. His depredations have caused permanent and irrecoverable damage to the historiography of the periods involved.