Complex sentence: Robert's brother Edward Bruce carried out a series of campaigns against English forces in Ireland and was declared High King, which, although ultimately unsuccessful opened the prospect of what has been characterised as "Pan-Gaelic Greater Scotia" under the Bruce dynasty.
Split into simpler sentences: Robert's brother Edward Bruce carried out a series of campaigns against English forces in Ireland and was declared High King. The campaigns in Ireland, although ultimately unsuccessful, opened the prospect of what has been characterised as "Pan-Gaelic Greater Scotia" under the Bruce dynasty.