Complex sentence: About 20% to 25% of the population died or emigrated, The Encumbered Estates Act of 1849 was passed to allow landlords to sell mortgaged land; many went bankrupt as their tenants could not pay any rent due to the famine.
Split into simpler sentences: About 20% to 25% of the population died or emigrated. Many landlords went bankrupt as their tenants could not pay any rent due to the famine.