Some Byzantinists, notably Dimitri Obolensky, suggested that the Arab expansion against the Khazars was motivated by a desire to outflank the Byzantine defences from the north, and envelop the Byzantine Empire in a pincer movement. However, this idea is rejected as far-fetched by modern scholars. As historian David Wasserstein comments, it is a scheme of extraordinary ambition, which "requires us to accept that Byzantium had succeeded already at this primary stage in persuading the Muslims that it could not be conquered", and furthermore that the Muslims possessed "a far greater knowledge and understanding of the geography of Europe" than can be demonstrated for the time in question. Mako likewise remarks that such a grand strategic plan is not borne out by the rather limited nature of the Arab–Khazar conflict until the 720s. It is more likely that the northward expansion of the Arabs beyond the Caucasus was, at least initially, the result of the onward momentum of the early Muslim conquests, with the local Arab commanders seeking to exploit opportunities, haphazardly and without any overall planning. The expansion may even have been in direct contravention to caliphal orders, repeating a frequent pattern during this period. From a strategic perspective, it is far more probable that it was the Byzantines who encouraged the Khazars to attack the Caliphate to relieve the mounting pressure on their own eastern frontier in the early 8th century, as indeed Byzantium profited considerably from the diversion of the Muslim armies northwards in the 720s and 730s, resulting in another alliance through marriage, between the future emperor Constantine V () and the Khazar princess Tzitzak in 733.