MANY THINGS HAPPENED IN THE SATYA YUG (ALSO KNOWN AS KRITA YUG)
1. SAMUDRA MANTHAN
The gods lost all their power and vitality after a curse by the sage Durvasa. To regain their strength and immortality, they sought Lord Vishnu's help. He advised them that the only way to obtain the Amrita was to churn the great cosmic Ocean of Milk (Kshirasagara).
2. DEATH OF HIRANYAKSHIPU AND HIS BROTHER
Shri Vishnu took the Narsimha avatar and varaha avatar to kill two powerful Asuras - Hiranyaksha and Hiranyakshipu, who terrorized the gods and were incredibly strong due to the vardaans given to them by Brahma.
3. THE TARAKMAYA WAR
This war / Yudh happened after the kidnapping of Brihaspati’s wife Tara by the Moon God Soma.
4. MATSYA AVATAR
Lord Vishnu incarnated as a fish to save Manu (King Satyavrata) from a great deluge (flood) and preserve the Vedas and all species for the next cycle of creation.