Complex sentence: The clauses relating to custom effected only a minority of the 600,000 tenant farmers in Ireland, therefore it was the clauses relating to yearly tenants unprotected by custom which formed the most important clauses in the Act.
Split into simpler sentences: The clauses relating to custom affected only a minority of the 600,000 tenant farmers in Ireland. Therefore, it was the clauses relating to yearly tenants unprotected by custom which formed the most important clauses in the Act.