Rome, under the Emperor Constantine, 312 AD.
Armenia was the first country to adopt Christianity as its official religion in the year 301 AD.
Vatican City
The Roman Empire(present-day Italy) was the first to establish Christianity as an official religion.
armenia
Probably the Palestine region although it was not the official religion at the time.
It's not the official religion. If you were raised in another country with a different religion, that religion would be considered the official one. It's all society based to help maintain control and order. It's a dying trend.
Armenia was the first to adopt Christianity as the state religion. King Tiridates III made Christianity the state religion in 301 CE, even before Christianity was officially tolerated by the Roman Empire.
No, Australia does not have an official "state religion", but the country was founded on Christianity. One of the provisions in Australia's constitution is the guarantee of freedom of religion for all, so many religions are now represented.
India does not have an official religion.
NO. Christianity really began with the followers of Jesus in the southwest Levant (Israel/Palestine) and had many of its doctrines codified in the Aegean region (Greece and Western Turkey). Armenia is famous in the history of Christianity since it is one of the first, if not the first, country to make Christianity its official religion. (There are arguments as to whether Georgia or Ethiopia beat Armenia to the punch of being the first country to make Christianity its official religion, but we are talking about decades here, not centuries of difference.)
Israel.
There is no "one world religion." There are many different cultures throughout the world and many different religions. Some nations have an official religion for their country, but there isn't a "one world religion" of any kind. Christianity is the most commonly practiced religion in the world, but it certainly isn't the ONLY religion of the world, neither is it the official religion of the world.