Well, the back story is about the Andromeda Initiative. It was a huge undertaking. The Milky Way civilizations decided to explore and colonize Andromeda. They built advanced arks filled with people from different species. These people were put into cryo - sleep for the long journey. Once they reached Andromeda, they expected to start anew. However, things didn't go as planned. There were already native species in Andromeda that were not exactly friendly. Plus, the technology they brought had some unforeseen issues, and they had to struggle to build their colonies and make a place for themselves in this new and strange galaxy.
The back story of Mass Effect Andromeda involves the journey to the Andromeda galaxy. The Milky Way races, facing various challenges like overpopulation and resource depletion, send out the Ark ships. These ships carry colonists in cryo - sleep to find a new home in Andromeda. There are different species on these arks, each with their own motives and cultures. The Initiative aims to establish a new civilization in this new galaxy, but they face many unforeseen difficulties upon arrival, such as hostile alien species and the challenges of terraforming planets.