Complex sentence: During the Great Irish Famine (1845--1851), Irish families were forced to emigrate from Ireland; by 1854, between 1.5 and 2 million people were forced to leave the country-about a quarter of the pre-famine population.
Split into simpler sentences: During the Great Irish Famine (1845--1851), Irish families were forced to emigrate from Ireland. By 1854, between 1.5 and 2 million people left Ireland-about a quarter of the pre-famine population.