Did the Buddha try to effect social change? This month is Buddhist Action Month in the UK when we try to be a bit more socially engaged. To quote from the website 


  Despite Buddhism's reputation for stillness and withdrawal from the
  world, UK Buddhists are engaged in a wide range of social-change
  projects, alleviating suffering at home and abroad


So leading on from this, I was wondering whether the Buddha promoted this kind of social engagement. Was the Buddha active in addressing political and social injustices of his time or did he more work within the social norms and bring about liberation in that way. I'm particularly interested in references to the Pali Canon to illustrate answers but answers from other traditions and texts would also be interesting.
Let me narrow down "engaged Buddhism" to "applying the Dharma to social and political injustices".

In the Kathavatthu Sutta, the Buddha did not prefer monks to engage in discussions concerning mundane things:


  Then the Blessed One ... addressed the monks: "For what topic of
  conversation are you gathered together here? ..."
  
  "Just now, lord, after the meal, ... we ... engaged in ... conversation about kings, robbers, &amp;
  ministers of state; armies, alarms, &amp; battles; food &amp; drink; clothing,
  furniture, garlands, &amp; scents; relatives; vehicles; villages, towns,
  cities, the countryside; women &amp; heroes; the gossip of the street &amp;
  the well; tales of the dead; tales of diversity, the creation of the
  world &amp; of the sea; talk of whether things exist or not."
  
  "It isn't right, monks, that sons of good families, on having gone
  forth out of faith from home to the homeless life, should get engaged
  in such topics of conversation ....
  
  "There are these ten topics of [proper] conversation. Which ten? Talk
  on modesty, on contentment, on seclusion, on non-entanglement, on
  arousing persistence, on virtue, on concentration, on discernment, on
  release, and on the knowledge &amp; vision of release.


At the same time, the Buddha advised the lay followers in the Sigalovada Sutta on how good friends should be. From here, I extrapolate that lay Buddhists can become good friends of their fellow members of society, and exhort them to be likewise. This can be one way to Engaged Buddhism.


  
  "Young man, be aware of these four good-hearted friends: the helper, the friend who endures in good times and bad, the mentor, and
  the compassionate friend.
  "The helper can be identified by four things: by protecting you when you are vulnerable, and likewise your wealth, being a refuge when
  you are afraid, and in various tasks providing double what is
  requested.
  "The enduring friend can be identified by four things: by telling you secrets, guarding your own secrets closely, not abandoning you in
  misfortune, and even dying for you.
  "The mentor can be identified by four things: by restraining you from wrongdoing, guiding you towards good actions, telling you what
  you ought to know, and showing you the path to heaven.
  "The compassionate friend can be identified by four things: by not rejoicing in your misfortune, delighting in your good fortune,
  preventing others from speaking ill of you, and encouraging others who
  praise your good qualities."