Making a thread on a small nation called Armenia, that you may or may not have heard of.

Why is it so special? Because it was the first state in the world to adopt Christianity as its state religion.

Modern Armenia within the red borders in the centre. It is known as Hayastan in the Hye (Armenian language)

I would suggest you to go through this book.
https://www.scribd.com/document/265220424/Zoroastrianism-in-Armenia

Prior to its conversion to Christianity, Armenia was a devout Zoroastrian land.

Atashgah (fire temple), Ani, Turkish Armenia.

The conversion happened during the Sassanid era (the last great Zoroastrian empire before Iran fell to Islam).
The Sassanids had overthrown the Arsacid dynasty of Parthian empire.

A branch of the Arsacid dynasty also ruled Armenia during that time.

The Sassanids who had overthrown the Arsacids were devout Zoroastrians but wanted only one school, Zurvanism to prosper at the cost of others. Invasion into Armenia forced the Arsacids into exile.

They would retake the throne back with some help from the Romans.

It was during this time (301 AD) that "Gregory the Illuminator" managed to convert the Armenian king Tiridates (Trdat) III to convert to his religion.

During a ceremony of worship of goddess Anahita, the king asked Gregory to offer a flower to the deity but the man refused. His anger only increased when he came to know his father's murdered was none other than the pastor's father. In anger, he had him imprisoned.

The king had fallen sick. He had a dream that only Gregory could cure him, and the man was released. As the man managed to cure the king, the devout Zoroastrian king proclaimed Christianity as the nation's state religion and made him his head priest.

Two Hindu temples built by princes from Ujjain were destroyed as per orders of Gregory and their priests massacred in cold blood.

Furthermore, Trndez (Tyarndarach), a fire temple and Vartavar (Vadarvar), a temple dedicated to water goddess Ashtgik were converted to Churches.