In the most recent centuries momentous events, which defined the century in Europe, happened around the 10th year: World War I in 1914, Napoleonic Wars ending in 1815, Acts of Union in 1707. Were there such events in every century AD or is it just a coincidence in recent times?
What do you mean by "the 10th year"? The examples you list doesn't seem to occur in the same year (and also Acts of Union is only arguably an event that defined a century in Europe).