In my mind, the Hundred Years' War (Crecy; Joan of Arc) are very much thoroughly medieval. On the other hand, Christopher Cokumbus' travels to America are very thoroughly "of modern times". Yet, these events are only 40 years apart.
Is the distinction bad history, or did something fundamental happen over the last part of the 15th c. that actually changes our view of people in that time period?
/u/thechao
You should read up on periodization and regionalization, see for example 1, 2.
The factual aspects of history (hopefully) are fixed. The perspective depends on context. In your case, you see the 100YW as a medieval war. Some view it as the start of the Military Revolution, see for example the well-cited work of Rogers and Clifford Clifford Rogers, thus putting it in Early Modern context.
Similarly for Columbus, some see it as the start of the Age of Exploration. Many see it as the culmination of the ages-old Iberian rivalry between Portugal, Castile, and to some extent Aragon. In this latter perspective, it is the result of developments in the medieval era, however fuzzy the definition is.
Keep this up as you continue to be critical of your own perspective, it's a great motivator to expand your knowledge and challenge your established biases.
Edit: thx /u/Rittermeister