1. The 20th century: This century saw World War I (1914-1918), World War II (1939-1945), and many other major conflicts such as the Korean War, the Vietnam War, and the Cold War.
2. The 17th century: This period saw conflicts like the Thirty Years' War (1618-1648), which raged across much of Europe, the English Civil Wars (1642-1651), and the War of the Spanish Succession (1702-1713).
3. The 6th century BCE: This time marked an extremely turbulent period involving various civilizations, notably the Neo-Babylonian Empire, Egypt, Lydia, Media, and the Roman Republic. Numerous battles and skirmishes characterized these years, including King Nebuchadnezzar's conquests throughout the region.
4. 14th century: Particularly noteworthy for the Hundred Years' War (1337–1453) between England and France, along with many regional conflicts and power struggles throughout Europe and Asia.
These are just a few examples of time periods known for wars and hostilities.