I'm sure much of it was done in jest. Especially as compared to typical American humour, British humour is much more sarcastic and self-depricating, so it's seems more natural to tease others as well.
Unfourtunetly some people are just ignorant *****, and you may have come into contact with some of them. Which is a shame.
And it's most likely not against American's themselves. Like, personally, I don't agree with a significant amount of foreign policits, just as I disagree with much of the UK's and other countries politics. If people allow this to colour their own perspectives of people them they are missing out...
And the language this is inhernetly British, sorry! People here are quite proud of their literary heritage and will be defensive about things like 'harbor' and 'harbour'. Again I'm sure it's not meant in a venemous way, but it's something quite ingrained in British culture. The accent shouldn't be a target though, American accents are lush! Many people are also targeted, whether their British or foriegn, for their accent as well. Britiain has a huge amount of reigional accents and dialects in relative to it's size, and it is a source of mocking for many people. I'm sure you will have also come across a lot of Scottish/Geordie/Scouse/Brummie jokes in your time here! If anyone says anthing hurtful just tell 'em, language evolves just like everything else so piss off!