Short answers, pulled from the story.
The Visigoths led by King Alaric breached the walls of Rome in the year 410. This event marked the beginning of the end for the Western Roman Empire after nearly eight hundred years of the city conquering the known world.
The Great Schism occurred in the year 1054 when the church in Rome excommunicated the patriarch of Byzantium. This permanent division separated the Latin West from the Greek East and was solidified by the Crusades including the Fourth Crusade in 1204.
Christopher Columbus set sail across the Atlantic Ocean in the year 1492. This voyage initiated the European colonization of the Americas and led to the Atlantic slave trade which transported 3.5 million African slaves to the Americas under the British Empire alone before its abolition in 1807.
The Inquisition was abolished in the 19th and 20th centuries during the French Revolution and the subsequent secularization of the Western world. This period hastened the separation of church and state and led to the secularization of the Western world where unchurched spirituality gained prominence over organized religion.
The Cold War began in the year 1947 and ended in the 1980s with the advent of Mikhail Gorbachev and the subsequent dissolution of the Soviet Union. This period divided the world into three distinct spheres including the First World analogous to the Western world and the Second World consisting of the Eastern bloc.
76.2% of Europeans identify as Christian in the modern Western world. Christianity remains the dominant religion in the Western world with 73.3% in Oceania and about 86.0% in the Americas also describing themselves as Christian.