1500s: In 1582, the Gregorian calendar is introduced in Catholic countries. This calendar is designed to replace the Julian calendar, which contains a ten-day discrepancy. The new calendar provides a more consistent and unified way to manage days, weeks, months, and the passing of years, since it is based on a close approximation of the actual length of time it takes the earth to revolve around the sun.

Today: Although many countries continue to maintain different religious and cultural calendars, the Gregorian calendar has become the universal tool by which all countries note the cycle of the seasons.

1500s: The Spanish king, Phillip II, attempts to invade England in 1587, after the execution of Mary, Queen of Scots. The conflict between England and Spain is largely due to the animosity of the Catholic Spanish for the Protestant English. However, the Invincible Armada, as the king named...