Cuba is a unique case. Fidel Castro could not trust some leaders because America makes efforts to win them over and bring Cuba under it's indirect control. Hence, Fidel had to install his brother.
The dynasties in countries like India, Bangladesh are not comparable to Cuba. Our dynasties are for power and to become rich.
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A leader can retain his/her charisma for years and years provided he/she behaves like leader. Unfortunately, many of the leader world over, as soon as they get power, they start enjoying it forgetting the welfare of people. Only very few leaders like Fiedel Castro did not succumb to such lure. For that reason, his every action is respected.