We no longer provide faction unlock requests. If you are a new player and under level 5, you have one free faction unlock which you can access from the faction select screen on the top-right corner of the deploy screen (after pressing play at the main menu). If you are over level 5, or you have already exercised your free faction unlock, then you will need to wait until a new war to pick a new faction.
Most wars last between 2-4 weeks. When a war is won, it enters into "Resistance Phase" for 1-3 days. After this phase has ended, a new war is started and all faction locks are reset.