Faction loyalty

It is important to consider when buying ships from the trade row that you are building a fleet or fleets. Unlike many deckbuilders, each human faction's fleet is loyal to its own. 

If another player has built a powerful fleet of one faction, you may strategically defend a key planet with a ship of that faction.

If you have bought a fleet of confederation ships, an opponent’s system with one confederation ship  defending is considered a friendly system.