The first time I really saw the opposing faction was around rank 9 in an area where each side was vying for 4 towers. There were a number of quests to complete in that little section, and some decent world pvp.
Retired: Inra-Dark Crag 40/40 Witch Elf
Retired: Hollow-Thunderlord 70 Warlock S1/S3 T4 SL/SL
Retired: Horknee-Thunderlord 70 Druid T4/T5 Feral