"Imperial pride and superiority" is quite loaded language and is I think a bit misleading here - the British government more likely saw themselves as defending the legitimate rights of their citizens against violations from another state.

It's a complicated issue and I'll try to clarify what this means - the commercial dispute over Opium had been fought for several years before the Opium war actually began. Essentially, the Chinese government banned the sale of opium, seized British citizens and their property and held them hostage before releasing them and destroying their opium. The opium dealers and other traders then retreated to the islands just south of Guangdong.

At this stage, the opium dealers received relatively little sympathy from the British government - in spite of their considerable lobbying and the importance of opium to the government of India's finances, the trade was opposed by the church and was highly controversial.

What followed was a long, messy dispute (over compensation for the opium destroyed and accusations that the British were continuing to sell opium, among a host of other issues) between the British consul and Lin Zexu, the Chinese official who was under huge pressure to stamp out the opium trade (which had become a catch-all explanation for an array of economic and moral problems in China among certain factions of Beijing officials) and to drive out the foreigners more broadly.

Put simply, Lin Zexu was under immense pressure - his entire career rested on his ability to make good on a promise to stamp out the opium trade within a few months. His tactics in forcing the British to make concessions consequently became increasingly confrontational and violent, with several threats of massacres of British citizens delivered to the consul and attacks on British settlements. This was what tipped the British government in favour of war (although it remained a controversial decision - Palmerston, the Foreign Secretary who ordered the invasion, was censured for it not long after).

That being said, the demands made in the treaty that ended the war went far beyond the quite narrow concerns that set it off - these can be found (here)[http://en.wikipedia.org/wiki/Treaty_of_Nanking].

The best source on the Opium War that I've come across is The Inner Opium War by James Polachek. Most of the detail above comes from that book.