>>64447477
First you need to define

>how willing is the attacker to commit atrocities
>how willing is the attacker to ruin infrastructure (compared to capturing int somewhat intact)
>how complete is the control of earth supposed to be

Depending on context, it changes drastically. If you´re fine with butchering 4 billion people and reducing half of earths infrastructure to utter rubble, things will look different. Things will also look different wheter or not you plan to install puppet government, or if you want to actively taker over in every single place, install off-world people and crush every resistance and insurgency.

Are you willing to strike a deal with Earth faction A against Earth faction B and C, or are we talking some outside force taking on a united earth

>>96851796
Why would Guardians be better fighters than Guardsmen? They're emergency militia, not warriors.