To my knowledge, for an Invasion to occur ones planets/cloud of influence must be less than one quadrant(is that the right term?) away. Since Balmorra is only a stone's throw from Syndicate space, we have the green light OOC wise to initiate an invasion. The order of invasion is important too, we can't simply roam into Corellia and take it, you have to move from planet to planet and cut a path to the capital if that's your end goal.
As far as bullying goes, it's not my intention to simply swarm smaller factions. However, the chips fall that the Republic and the Sith have the largest faction and any invasion between them and another faction (besides their large counterpart) would be considered bullying by your logic. While I was apart of staff, and Tef and Tegs can attest to this, I motioned that there be some sort of etiquette for invading factions with smaller populations. But there's no official ruling yet.