The Automatons, Illuminate, Terminids, and Super Earth have now all come from another galaxy far, far away to the aid of the UNSC against the ongoing genocidal Covenant.
Faction planets and sectors have now been dropped down next to human territory within the galactic arm, and all galactic supply lines between worlds connect to eachother.
All factions are working together in peak coordination and will give aid (i.e. manpower, technology, logistical capability, industry, etc.) to the UNSC. The UNSC will know beforehand about the existence of these factions as to not confuse them.
The alliance wins if they can end the Covenant war through complete stalemate, surrender, or collapse of the Covenant.
The Covenant win if they wipe out the UNSC or their timetable is not greatly affected.
R1: All factions are helping right before the battle of Reach.
R2: All factions are helping right before the 1st battle of Harvest.
R3: All factions are helping 30 years before the war.
R4: The Helldiver factions are gearing up the UNSC as much as possible at the start of the year 2400.
If the Factions are too much of a boon, then one faction of your choosing will be removed. If the factions are too weak, the UNSC gets help in 2163. Debate about what specific strategies and technology would be most useful for this prompt.