As leader of Zimbabwe, Robert Mugabe has survived longer than Stalin in the Soviet Union and Mao in China. If its coming to an end -- which seems likely given his apparent inability to emerge from house arrest after the military took charge -- its worth reflecting on the mistakes he made to end such a remarkable run. Daniel Treisman, a UCLA political scientist, argued in a recent paper that most dictators fall for reasons proving that they are all too human: hubris, a propensity for needless risk, liberalization impulses that lead to a slippery slope, picking the wrong successor, counterproductive violence. Mugabe, 93, is no exception; he groomed the wrong person to succeed him and relied too much on his military. When he tried to change his pick, the generals decided theyd had enough. Almost throughout Mugabes 37-year rule, Emmerson Mnangagwa -- like Mugabe, a veteran of the war for Zimbabwes independence from the UK -- was the dictators closest ally and aide. The countrys first security minister, he ran the special units that suppressed tribal resistance to the rule of Mugabes party. These units forced villagers to dance on the freshly filled graves of their relatives, chanting pro-Mugabe slogans, Heidi Holland wrote in "Dinner with Mugabe," an account of his transformation from a national liberation icon to an autocrat. Later on, in the late 1990s, when Zimbabwe intervened on the governments side in the Second Congo War, Mnangagwa built strong ties with the military, helping it gain mining concessions in exchange for propping up President Laurent-Desire Kabila. Mnangagwas political ambitions grew, and in 2005, Mugabe slapped him down, taking away his senior post in the ruling Zanu-PF party following a play for the vice presidents post. But he survived the demotion and ended up rising to the vice presidency anyway in 2014. It was clear that, despite his lack of political prowess -- hes lost elections twice in his home constituency -- Mugabe saw him as a potential successor. As Mnangagwa demonstrated his staying power, built ties and accumulated favors in various parts of the Zimbabwean establishment, Mugabe was growing more dependent on the military. Charles Mangongera, a Zimbabwean researcher, wrote in a 2014 paper: As the president’s authoritarian grip on the state has been gradually slipping in the face of growing opposition, the military has grown more and more involved in politics. Military elites have gained institutional vetoes and blocked the country’s transition to democracy through the militarization of key state institutions and the use of state-sanctioned violence against Mugabe’s challengers. In return, those military elites have been rewarded with lucrative government contracts, access to prime land, mining concessions, and other perquisites from the predatory state presided over by the Mugabe regime. The Zimbabwe Defense Forces are not the kind of military that, at critical moments, steps in to guarantee normality and adherence to governance traditions, as the Turkish military did more than once in the 20th century. The ZDF are inextricably linked with Zanu-PF, but not necessarily with Mugabe. As the aging dictator became more and more frail, often falling asleep in public, Constantine Chiwenga, the ZDF commander, became known as a Mnangagwa ally. So, when Mugabe fired Mnangagwa earlier this month, accusing him of disloyalty, and when it became clear the dictator would like his wife Grace to serve as vice president and take over from him, Chiwenga made his move, promising to stop "those bent on hijacking the revolution." The military takeover in Harare took place the following day, on Tuesday. Theres little to celebrate about it. Grace Mugabe, with her violent temper and love of luxury, probably wouldnt be a great president. Mnangagwa, 75, is hardly an improvement. Observers have described him as a cruel, spiteful man. "The opposition candidate who defeated him in Kwe Kwe Central after a bitter campaign in 2000 narrowly escaped death when Zanu-PF youths who had abducted him and doused him with petrol were unable to light a match," Holland wrote. Zimbabwe, which has gone through traumatizing violence and economic upheaval under Mugabe, doesnt have much to expect from the military intervention. This kind of change, born of palace intrigue rather than popular resistance, means things stay the same or get worse for them. The new dictator will seek to make sure hes more coup-proof than his predecessor, and that may mean more violent suppression. For autocrats elsewhere, however, what happened in Zimbabwe can be a useful lesson. A longtime associate with succession ambitions cannot wait forever for a dictator to die. If hes allowed to build up power, and especially befriend the most powerful generals, a dictators days in power are numbered. He wont be allowed to change his mind on the succession, either. Constantly shaking up the security apparatus and the political leadership allowed Stalin and Mao to die in office. An early decision to establish a dynasty worked well for Kim Il Sung. Mugabe wont be joining the ranks of these undefeated dictators because hes been negligent. Its only human, especially after almost four decades in power. Bloomberg