The Kurultai, however, required the presence of the senior members of the tribes participating, who were also military leaders. Thus, the deaths of Ögedei and Möngke in 1241 CE and 1259 CE, respectively, necessitated the withdrawal of Mongol leaders (and troops) from the outskirts of Vienna and Venice (in 1241) and from Syria (in 1259), hamstringing military operations against the Austrians and Mamluks that might otherwise have continued.