 Complete the following phrase:  Neither empire was given any chance to recover, as within a few years they were struck by the onslaught of the Arabs newly united by Islam, which, according to Howard-Johnston, can only be likened to a human tsunami. According to George Liska, the unnecessarily prolonged ByzantinePersian conflict opened the way for Islam. The Sasanian Empire rapidly succumbed to these attacks and was completely conquered. During the ByzantineArab wars, the exhausted Roman Empires recently regained eastern and southern provinces of Syria, Armenia, Egypt and North Africa were also lost, reducing the Empire to a territorial rump consisting of Anatolia and a scatter of islands and footholds in the Balkans and Italy. These remaining lands were thoroughly impoverished by frequent attacks, marking the transition from classical urban civilization to a more rural, medieval form of society. However, unlike Persia, the Roman Empire ultimately survived the Arab assault, holding onto its residual territories and decisively repulsing two Arab sieges of its capital in 