Why do these two factions of Irish Loyalists hate each other so? Aren't they both striving for the same cause?

Also, can someone give me a brief history of the Irish struggle to free themselves from Britain. Links, videos, whatever would be appreciated.

I don't know very much about the history of the conflict. Which saddens me, as I am part Irish, and I know so much about my other heritages, but I know jack shit about the Irish part of my family's past.