There are four playable factions here in ST:I. The Federation, Romulans, Klingons and Cardassians. I’m probably leaning towards The Federation, but they cannot declare war on anything. They are all about incorporating independent factions into the Federation. I have gone entire dynasties of Stellaris with DOWing since I love exploring and colonizing the game, so that won’t be an issue. This is set in the era of TNG. Basically the Federation is all about diplomacy, the Romulans about intrigue, the Klingons about combat and the Cardassians about power.
Here's info about the game from Paradox:
https://www.paradoxinteractive.com/games/star-trek-infinite/about
Please note that this game is just released two months ago, so there is no ST:I wiki yet. I am just doing this myself.