In Distant Worlds Legends, alien races may be introduced into your empire by migration and conquest. There are various ways to treat them. How will they affect the player's empire? What's a good strategy to deal with them?
There are various ways to benefit from aliens living in your empire. Depending on the race of the alien population they might give your empire some kind of bonus. For example certain races reduce the cost of ship maintenance, however the alien population needs to be big enough for a bonus to apply.
Some alien races make better soldiers than others. For example the Mortalen are better suited for combat than humans. So if you have a planet full of Mortalen's recruiting your troops from there will increase the combat power of your units.
Another way to exploit an alien race is by enslaving them. Enslaving an alien race will give you a GDP boost on the planet where they are enslaved, on the flip side this will anger any empire whose population is composed of the race you are enslaving.
A downside of having aliens live within your borders is that they become unhappy if you declare war on an empire of their won race. For example if you declare war on a Securan empire any Securans living in your empire will become unhappy.