Complex sentence: The new Jamaican dollar (and the Cayman Islands dollar) differed from all the other dollars in the British West Indies in that it was essentially a half-pound sterling; the other dollars either began on the US dollar unit or the Spanish dollar unit.
Split into simpler sentences: The new Jamaican dollar (and the Cayman Islands dollar) differed from all the other dollars in the British West Indies in that it was essentially a half-pound sterling. All the other dollars either began on the US dollar unit or the Spanish dollar unit.