Short answers, pulled from the story.
The modern era, also called the modern period, is the current historical period of human history. It was originally applied to European and Western history for events after classical antiquity and the Middle Ages, often from around the year 1500.
The year 1500 is an approximate starting point for the modern era, because many major events reshaped the Western world around then. These included the fall of Constantinople in 1453, Gutenberg's moveable type printing press in the 1450s, Columbus's voyage in 1492, and Luther's Ninety-five Theses in 1517.
Since the 1990s, historians have more often called the span after the Middle Ages and up to the 19th century the early modern period. The modern period is now more often used for events from the 19th century until today, with the split defined by the French Revolution and the Industrial Revolution.
The common definition of the modern period is often associated with the French Revolution, the Industrial Revolution, and the transition from nationalism toward the liberal international order. It has been a time of significant development in science, politics, warfare, and technology.
Optimism and the belief in constant progress have been criticized by postmodernism, while the dominance of Western Europe and North America over the rest of the world has been criticized by postcolonial theory. The brutal wars of the era and the loss of strength of traditional religious and ethical norms drove many reactions against modern development.
World War II took place from 1939 to 1945 and was the largest and deadliest war in history, with possibly around 62 million deaths. It ended with the atomic bombings of Hiroshima and Nagasaki and Japan's surrender on the 2nd of September 1945, after which power shifted to the two new superpowers, the United States and the Soviet Union.