Who are some world leaders that use nationalism to promote their agenda?
It might be easier to make a list of the world leaders who do not use nationalism to try to advance their agendas. This is a very common thing for leaders to do.
Many of the leaders who make these claims are despots who try to use nationalism to gather support for themselves and to reduce levels of anger among their people. The Venezuelan leader Hugo Chavez, who died today, was a good example of this. He liked to portray himself as fighting for the Venezuelan people against American imperialism. Fidel Castro of Cuba did this as well. The Kim family in North Korea has done similar things.
Even less despotic leaders do this, however, the leaders of China like to fan the flames of anti-Americanism and of anti-Japanese feeling. British politicians have been competing lately to see who can sound more skeptical of the European Union. In the United States, leaders use nationalist rhetoric frequently as well. We are exhorted to believe that we are a unique country and we are encouraged to think, for example, that Democratic politicians lack national pride.
In all of these cases, nationalism is used to bolster support for leaders and, thereby, to advance their agendas.