Explain the challenges of not having a unified global calendar. what problems does that create?

A unified global calendar is the Gregorian calendar that entails the weekday of any given date (day, month, year)

Different nations have different calendars according to their religion, cultures, custom, belief etc

The problem associated with not having a unified global calendar includes:

Read more about global calendar

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Challenge of not having a unified global calendar.

Explanation:

Different nations have different calendars according to their religion and cultures. Each country has its customs to follow with a holiday on that day for celebrations. By having a separate calendar, it creates problems when markets, business, and stock markets are close in a country when the rest of the world is working on that particular day. For tourists, it creates a problem when they are not aware of the national holidays of a country when they find historical sights and museums close. The unified global calendar helps businesses, tourists, and trade.

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.

ayatollah khomeini can best be described as the leader who declared iran to be an islamic republic.