You're oversimplifying the situation to the point of absurdity. Yes, the majority was Northern Irish vs. Northern Irish, but it was between Catholic and Protestant, with the Protestants being mainly allied to Britain and the Catholics mainly to Ireland. The Catholics were upset with the institutionalised discrimination against them by the British-led institutions, and the Protestants were in favour of supporting those institutions. Clearly British influence had everything to do with the issue as the number of Protestants in Northern Ireland would have been drastically lower without British settlement and influence. The police were indeed mainly Northern Irish - and Protestant at that, which really didn't help the issue one iota. The British government refused to acknowledge the issues raised by the Catholics, and definitely refused to address them (as they didn't exist, according to the British government), hence the continuous rise of the IRA, and then the Protestant groups which gained power in order to fight them and support the Protestant cause. But I guess if you ignore pretty much everything it was as simple as you stated.