Complex sentence: Historically a part of County Durham, now the county of Tyne and Wear, along with South Tyneside it lies on the southern bank of the River Tyne opposite Newcastle upon Tyne and together they form the urban core of Tyneside.
Split into simpler sentences: Historically a part of County Durham, but not part of it anymore it is now the county of Tyne and Wear, along with South Tyneside. It lies on the southern bank of the River Tyne opposite Newcastle upon Tyne and together they form the urban core of Tyneside.