If all the nations around the world put up a fight together against the invaders, it might last a day or less and we'll lose. We don't know anything about their technologies, weaponry, and ways of communication. If we use nukes, we'll be hurting ourselves, and the environment for many years.
Or we'll just give up without a fight. No doubt that the invaders will have the entire world surrounded.
If we can't match their technologies with our own, then it is already a lost for Earth. We still rely on fossil fuels and projectile weapons.
Our maximum speed for traveling to the nearest star: Proxima Centauri.
slowest: Ion drive propulsion, 81,000 years
Fastest: Gravitational assists, 19,000 years
(theoretical) Nuclear Pulse Propulsion: 85 years
4.22 light years
