For this achievement, you will need to encounter someone name Elek. Elek is part of a group called the Coalition and want to make a name for himself. Elek will have several missions for you over multiple runs.
The first mission will be to raid an outlaw station. This mission is pretty self explanatory. Go in, destroy some turrets and wait for Elek to take the loot.
The next time you meet him he will have a different type of mission. This time you will have to raid G&B transport ships. What you are supposed to do in this mission is to destroy the cargo containers on the ship itself before it escapes. There are 3 ships, each with 2 possible supply drops. I don't know what happens if you don't get all the supply drops so watch out. Also, don't destroy the transport ships.
Elek's next mission will be to get a new outpost for the Coalition. There are 3 Grey Goos at this location which you have to destroy. Elek will give you the advice to use a damage limiter right before you kill a Grey Goo (Grey Goo will explode and swarm you so watch out).
Your next mission from Elek will be to kill a hostile outlaw chief named Zack. Once you enter the zone you will get a call from Elek. He will tell you to wait a bit before engaging Zack. After a little bit Zack will be on his own and you can take him out. Zack will fly an outlaw bomber ship. If you attack Zack before he is on his own or when you take him out, Elek en his Coalition buddies will join the battle to take care of the remaining enemies.
The last mission from Elek will be to wipe out an outlaw clan, the Phantom Retaliators because they are occupying Coalition space. Once you enter the zone, Elek and the Coalition will be waiting for you. The objective here is to destroy all the enemy outlaws. Elek and the Coalition will follow you and help you deal with the outlaws.
After clearing the outlaws in the last mission for Elek, the Coalition will be stronger then ever and you will have unlocked an achievement. Elek and the Coalition will now occasionally help you in fights.