As with many Arab dynasties, the lack of a generally accepted rule of succession was a recurrent problem with Rashidi rule. The internal dispute normally centered on whether succession should be horizontal (i.e. to a brother) or vertical (to a son). These divisions within the family led to bloody infighting. In the last years of the nineteenth century six Rashidi leaders died violently. Nevertheless, The Al Rashid family continued to rule and fight together against Ibn Saud. Saudi Arabia- The first twenty years of the 20th century on the Arabian Peninsula featured a long-running series of wars as the Saudis and their allies sought to unite the peninsula. Some members of the Rasheed family left the country and went into voluntary exile, mostly to Iraq. Iraq The Shammar is Iraq's largest Arab tribe, along with the Jubur, with more than 1.5 million members. Under the leadership of Banu Mohamad, known as Al Jarba, there was a massive exodus into Iraq. Most of the Shammar in Iraq gave up their nomadic lifestyles to settle in major cities, especially the Jazirah plain, the area between the Tigris and Euphrates from Baghdad to Mosul. Droughts triggered several migrations of Shammar into Iraq, which, according to the Ottoman census upon its annexation, had only 1.5 million inhabitants. The Shammar took over the Jazirah after displacing Al-Ubaid tribe. According to Sheikh Abdullah Humaid Alyawar, the son of the sheikh of Shammar, in Iraq the total population of Shammar is estimated to be more than 1.5 million. The Shammar Al-Sayeh, a tribal confederation of tribes from Shammar, is the branch of Shammar who were independent of Aljraba's authority. Shammar is composed of groups such as Al-Zuhairy and Al-Towej in Najaf. The Shammar became one of the most powerful Iraqi tribes, owning vast tracts of land and provided strong support of the Hashemite monarchy. Shammar power was threatened after the overthrow of the monarchy in 1958 by Abdul-Karim Qassem, and the Shammar welcomed Ba'athist rule. After the overthrow of Saddam Hussein, Ghazi al-Yawar, from the Al Jarbah clan, was unanimously chosen as interim president. Ghazi Al-Yawar's uncle is the current Sheikh of Sheikhs of Shammar. Syria The Shammar tribe have been present in Syria since at least the 1920s when rivalry between Syrian and Iraqi Shammar culminated in violence reported by the League of Nations in 1926. Syrian Shammar Sheikh Diham al Hadi, the paramount Shammar sheikh