Where did a hotbed of hotbed nationalists and ethnic rivalries exist in world war 1 in the early 1900S?

In Ireland, between the Protestants and the Catholics.

Protestants (Unionists) wanted to stay part of the British empire as they were loyal to the Crown and they benefited economically (free trade with Britain) as well as religiously they were safe as Britain was Protestant too.

Catholics (Nationalists) were split into Extremists who wanted to be completely separate from Britain and were willing to use violence to get it & the Moderates who were opposed to Britain but saw no use in getting physical. They settled for Home Rule as their aim - Irish control over education, taxes, roads etc. but Britain could still have power over trade & war.

Also Catholics felt uncomfortable in a Protestant country. (75% Catholic in Ireland)

Irish customs & language were classed as rough and the country was being anglicised.

The Irish economy was spiralling downwards and it was still an argricultural country and Britain wasn't doing enough to support them.

The people in control of Ireland were barely ever in the country and any new law's had to go through The House of Lords in London, who had the power to veto anything they didn't like, being conservative & protestant this was a lot of the motions the Catholic Irish proposed.