Answer:
Weight loss & diarrhea in my opinion.
The Arabs expansionist movement started with the Arabs defeating the Byzantines at the <em>Battle of Yarmouk</em> - in August 636 along what is today the borders of Syria and Jordan and Syria and Palestine. The win of the Arabs ended the Byzantine rule in Syria and this battle is known as the most decisive battle of military history.
Later in 650 the Arabs conquest<em> Persia and marked the end of the Sasanian empire of Persia and the decline of the Zoroastrian religion.</em> They had liberal policies and made population free to convert to Islam or not. This made the place easier to conquest and less prone to rise up against the new government.
The empire continues to grow throughout Europe, leading to the <em>conquest of parts of the Roman Empire</em> but the <em>losses in Mesopotamia and Syria started the decline of the Arab expansion with minor successes of the Byzantines in 1055.</em>
