Similarly, the spread of Arabic across a large part of the world was entirely coincident with the spread of Islam. This slide shows Islam at about its greatest extent at the end of the 15th Century (though the Iberian Peninsula had been lost by then). But with the subsequent decline of Islam, Arabic has ceded much of its former common language status and has split at the margins into mutually incomprehensible vernaculars.

We see therefore that however forcefully a language might be established, as by government decree, it will not endure without popular acquiescence. This is always worth bearing in mind, since there may be strong economic and political arguments in favour of the establishment of a universal language at some stage. There are many instances where a language has been imposed without consent, and a reaction to the status quo ante has been the result.