Sort of. We had to change dates because people were using too many leap years.

So let's start at the beginning. For all intents and purposes today, we use a modified Roman calendar. Originally, supposedly, the Roman used a 10 month (Martius, Aprilis, Maius, Junius, Quintilis, Sextilis, September, October, November, and December) calendar of 304 days. These named months were followed up by an unnumbered winter period. The priests would simply wait about 60 days and announce when the new year started. This was supposedly modified by King Numa. He added February and January and lengthened the year to 355 days.

I say "supposedly" as we have no records directly from the time period. We only have Romans talking about what their anscestors did hundreds of years earlier. Numa is considered by most historians as a mostly mythical figure. So when we say "Numa" reformed the calendar, it's like saying that "King Arthur" did it. So who knows if the 304 day year ever really existed.

But at some point a 355 day calendar was adopted. That is of course about 10 days less than the 365.2425 length year we currently have. So every now and again the priests would insert an extra month called either Intercalaris or Mercedonius. There was no hard and fast rule as to when these would be inserted, and the priests could be bribed. So if you were an consul and wanted an extra month of rule, they were amenable to adding one. But the leap years were considered unlucky, so some men didn't want to have the extra month and so bribed the priests to not add one. And bribes or not, no priest would add a month in a time of trouble. So for example there were no leap years at all during the 17 year long Second Punic War.

The whole thing was something of a mess. In 45 BCE Julius Caesar reformed and regularized the calendar. As Pontifex Maximus he was the head of the Roman religion and so it was under his preview to do so. This was separate from his authority as a civil leader. He made the year 365 days long. He also added a single leap day to February every four years. This probably sounds very similar to what we use today. So you can thank Julius Caesar for the modern European calendar. In order to bring the system into synch with the seasons, 46 BCE was 445 days long and had three extra calendar months.

Of course the Julian Calendar has one little problem, the year isn't exactly 365.25 days long. By the 16th century the calendars were a couple of weeks out of synch. Easter wasn't happening when it was supposed to. Instead of March 21st as mandated by the ecclesiastical calendar, the Spring Equinox was happening on March 10th. So in 1582 Pope Gregory mandated that the calendar would skip from October 4th to October 15th. He also made a modification to the rules. Under the new rules, every year divisible by 4 would be a leap year, unless it was also divisible by 100 in which case it wouldn't be a leap year, unless it was also divisible by 400 in which case it would be. So 1600 was a leap year. But 1700 wasn't.

This Gregorian calendar has become the most common calendar in the world and it is the calendar we use today. But it took a while. Most Catholic countries adopted the calendar in 1582. But Protestant and Eastern Orthodox didn't exactly jump when the Pope said frog. So for example France and England were using different calendars until 1752 when the United Kingdom adopted the Gregorian Calendar. Russia didn't adopt it until 1918. Which can make Russian history really difficult to follow at times. The October revolution? That took place in November.

So yes Gregory XIII's calendar reform did cause us to change dates.