User blog comment:Sergeant Michael/Would the modern worl be able to survive a Covenant attack./@comment-104730-20131013002321

Not a chance in hell of a sustained resistance. I don't think there would even be any successful tactical defenses. Human forces, as it stands, lacks any ability to engage large orbital targets - ICBMs would be about the only weapon systems that are able to engage. But ICBMs are decidedly suborbital - and would require a parabolic intercept trajectory to hit a warship, and that seems to be exceedingly difficult to. And any nukes that miss will end up coming back to the surface, working perfectly. And such, Covenant orbital forces can simply glass organized resistance/population centers. So they essentially have air and space superiority (once they know out the main military airfields, which deprives air forces of spare parts and armaments should they relocate to civilian. Not to mention that Earth fighters are likely highly outclassed by Covenant weapons.

Ground warfare would be more balanced, but given the lack of air superiority, human forces would be overrun and very quickly routed. Not to mention orbital weaponry to provide support

So, its a no-brainer - Earth lacks the ability to even survive such an occurance.