You would think the logistics of global life would be a nightmare if every country had a different calendar, and you would be sort of right. A few countries do still use calendars that aren't the Gregorian, and we manage somehow, but they usually have pretty good reasons beyond "It just feels like the Catholics are up to something."
It might seem impossible for a calendar to be a hot-button political issue -- it just tells us when the days are. But when Pope Gregory XIII commissioned the development of the Gregorian calendar in the 1500s, which corrected the disastrous problems with the Julian calendar that eventually placed holidays like Easter in the completely wrong season, it threw the whole Western world into turmoil, mostly just because it was decreed by a Pope.
Catholic countries like Italy and Spain were like "Cool, new calendar," but Protestant countries like Germany and Britain accused the Catholic Church of trying to use this new calendar system to reassert Catholic control over the world, if only in the smallest ways. Like, so small, you guys. Others pushed back against what they saw as "the imposition of a true global interactive system and the acknowledgment of a new global reality" because medieval Europe had just zero chill. Some countries, specifically Russia and Greece, dug in their heels and refused to adopt the calendar until the 20th goddamn century.
Arguably the country with the least chill, unsurprisingly, was Britain, where Queen Elizabeth I actually wanted to adopt the new calendar until her bishops told her exactly where she could go with her hell chart, which was apparently something you could tell a queen back then. When the country finally made the switch in 1752, it's said there was rioting in the streets by people who were outraged by the requirement to erase 11 days to sync up their calendars (in their case, skipping from September 2 to September 14), for normal reasons like the complication of payroll systems and legal matters as well as weirder ones like the incredibly 18th-century belief that Parliament had actually brought them 11 days closer to death. Obviously, if Parliament had that ability, they would have done it much sooner.
Top image: The Bridgeman Art Library/Wikimedia Commons