Buddhism to change the world According to Buddhism, should one change oneself or change the world and why.
The Buddha did not intend monks to participate in politics, as seen in DN 2:


  "Whereas some brahmans and contemplatives, living off food given in
  faith, are addicted to talking about lowly topics such as these —
  talking about kings, robbers, ministers of state; armies, alarms, and
  battles; food and drink; clothing, furniture, garlands, and scents;
  relatives; vehicles; villages, towns, cities, the countryside; women
  and heroes; the gossip of the street and the well; tales of the dead;
  tales of diversity [philosophical discussions of the past and future],
  the creation of the world and of the sea, and talk of whether things
  exist or not — he abstains from talking about lowly topics such as
  these. This, too, is part of his virtue.


However, the Buddha did intend for lay people to participate in constructive nation building, in accordance with the Dhamma in DN 16:


  At that time the Venerable Ananda was standing behind the Blessed One, fanning him, and the Blessed One addressed the Venerable
  Ananda thus: "What have you heard, Ananda: do the Vajjis have frequent
  gatherings, and are their meetings well attended?"
  
  "I have heard, Lord, that this is so."
  
  "So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline.
  
  "What have you heard, Ananda: do the Vajjis assemble and disperse
  peacefully and attend to their affairs in concord?"
  
  "I have heard, Lord, that they do."
  
  "So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline.
  
  "What have you heard, Ananda: do the Vajjis neither enact new decrees
  nor abolish existing ones, but proceed in accordance with their
  ancient constitutions?"
  
  "I have heard, Lord, that they do."
  
  "So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline.
  
  "What have you heard, Ananda: do the Vajjis show respect, honor,
  esteem, and veneration towards their elders and think it worthwhile to
  listen to them?"
  
  "I have heard, Lord, that they do."
  
  "So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline.
  
  "What have you heard, Ananda: do the Vajjis refrain from abducting
  women and maidens of good families and from detaining them?"
  
  "I have heard, Lord, that they refrain from doing so."
  
  "So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline.
  
  "What have you heard, Ananda: do the Vajjis show respect, honor,
  esteem, and veneration towards their shrines, both those within the
  city and those outside it, and do not deprive them of the due
  offerings as given and made to them formerly?"
  
  "I have heard, Lord, that they do venerate their shrines, and that
  they do not deprive them of their offerings."
  
  "So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline.
  
  "What have you heard, Ananda: do the Vajjis duly protect and guard the
  arahats, so that those who have not come to the realm yet might do so,
  and those who have already come might live there in peace?"
  
  "I have heard, Lord, that they do."
  
  "So long, Ananda, as this is the case, the growth of the Vajjis is to
  be expected, not their decline."