Complex sentence: Moreover, the vast majority of the British population were effectively taxed without representation as, due to limited suffrage, half of the Parliamentary seats in England and Wales at that time were elected by a total of less than 12,000 men out of millions.
Split into simpler sentences: Moreover, the vast majority of the British population were taxed without being represented in Parliament. Half of the Parliamentary seats in England and Wales at that time were elected by a total of less than 12,000 men out of millions.