By the beginning of the 20th century, the Caribbean islands enjoyed greater political stability. Large-scale violence was no longer a threat after the end of slavery in the islands. The British-controlled islands in particular benefited from investments in the infrastructure of colonies. By the beginning of World War I, all British-controlled islands had their own police force, fire department, doctors and at least one hospital. Sewage systems and public water supplies were built, and death rates in the islands dropped sharply. Literacy also increased significantly during this period, as schools were set up for students descended from African slaves. Public libraries were established in large towns and capital cities.