William was related to the Stuarts by birth and through marriage.
His support in England seems to have come mainly from Whigs in London. He was also backed by the Pope who held a mass for him at the time of the Battle of the Boyne. Vienna was illuminated after his victory. It has been said that the Battle of the Boyne was the last European war on British soil.
Scotland in particular suffered from William's activities up there culminating of course in the Glencoe massacre.
His 'finest' achievement was the creation of the Bank of England. He invented or rather copied the idea of creating money out of thin air. Or rather thin paper. All to fight his wars.
http://www.bbc.co.uk/programmes/p00vpwhd