Complex sentence: The Ionian Bank (IB) was a British overseas bank that investors established in 1839 to operate in the Ionian Isles, which was then a British Protectorate, it was also the central bank of the United States of the Ionian Islands.
Split into simpler sentences: The Ionian Bank (IB) was a British overseas bank that investors established in 1839 to operate in the Ionian Isles, which was then a British Protectorate. It served also as the central bank of the United States of the Ionian Islands.