A different take on the preparation to retake Earth

In forgotten ages past, two near eldritch forces vied for the very life essence of the Galaxy. Unknown to the young races, that war is still ongoing. how can the UNSC, the Citadel Council or the Covenant hope to stand against such forces, when they are still embroiled in their own petty squabbling? How could they hope to survive the War of the Old Ones?

Before the Protheans or Forerunners, there was a war between Titans. That war is still ongoing. In the face of such forces, what could the UNSC, the Citadel Allience or the Covenant do; especially when they are embroiled in their own wars with one another?