How would you become an interstellar power in post-integration earth?

Hey guys, I have been thinking about something ever since I started reading system apocalypse stories. Imagine you have secured control of a post-integration earth, either created an empire or federation. You discover their are other system integrated worlds in the galaxy. You seek to conquer and/or establish diplomacy with these worlds. How would you go about becoming an interstellar power?

Would you use the system sanctioned teleport system with its limits on troops, levels, time limit and challenge required to stabilise the link. Would you work to develop portal magic and establish your own gate network? Or would you, through the use of magic and/or technology build a fleet of spaceships and colonise space?

Or do you have your own idea to become an interstellar power.