What happened to October 5th-October 14th?

    In some places the days from October 4th, 1582 to October 15th, 1582 don't exist in history.  On February 24th, 1582 Pope Gregory XIII introduced a decree called the Gregorian Calendar (otherwise known as the Western Calendar or the Christian Calendar). This proposal was accepted by Spain, Portugal, Italy, and the Polish- Lithuanian Commonwealth. (Spanish and Polish territories adopted it later do to delayed communication.)

    The Gregorian Calendar was proposed to make up for the roughly 11 minute lag in the current calendar. This would have resulted in around 3 days per 400 years. This was of concern of the pope because it was affected Easter. Easter is set on the Sunday following the full moon prior to the spring equinox. Since the variation in the actual time and the current calendar the day of the equinox had changed from the semi-set March 21st to March 11th since Roman times. 

   Although this calendar was not adopted by all countries immediately, it was followed but vast acceptance over the following centuries. It is now used by a vast majority of countries and many that don't use it solely use it alongside their primary calendar.