HERRICK
The USofA was hurting, as was most of the West, from 9/11. The Govt had to do something and try and track down the AQ people responsible. Britain lost 67 of its people out of ~3,000, so for us it was not such a big deal; but for our chosen lead in the financial sector it was pretty bad. It also affected the aviation sector that we had a big stake in plus also the insurance claims for this attack were the biggest in history. So something had to be done about Afghanistan (and the western half of Pakistan that borders it) and as others have said on here, our involvement was invited later. However, Ahmed Shah Massoud had asked the European Parliament for help in Afghanistan 6 months earlier from 9/11 stating that " the Taliban and al-Qaeda had introduced 'a very wrong perception of Islam' and that without the support of Pakistan and Osama bin Laden, the Taliban would not be able to sustain their military campaign for another year. Massoud warned that his intelligence had gathered information about an imminent, large-scale attack on U.S. soil". Unfortunately, this plea for help by Massoud was ignored and the rest, as they say is history. But if 9/11 hadn't happened would Afghanistan enjoyed such unified support Internationally? However, if Op HERRICK and the Afghan ops hadn't happened then I am convinced that the world would have been a worse place than it currently is. Op HERRICK (and TELIC) are not the sole reason for the rise of ISIS. Just like I said before, inaction in Syria hasn't worked out too well either!
LJ - I've heard a million and one reasons for the UK presence in Afghanistan ranging from denying terrorists space to train, all the way through to women's rights and drugs. After 9/11 the USA invoked article 5 of the NATO treaty and off we went as members of NATO. I don't understand why that was so difficult to explain to the British public....
Iraq - different story.