Complex sentence: The native Gaelic Irish were therefore viewed as an alien force in the city and suspicion of them was deepened by continual raids on Dublin and its environs by the O'Byrne and O'Toole clans from the nearby Wicklow Mountains.
Split into simpler sentences: The native Gaelic Irish were therefore viewed as an alien force in the city. Suspicion of them was deepened by continual raids on Dublin and its environs by the O'Byrne and O'Toole clans from the nearby Wicklow Mountains.