Take the civilization 20 light years away, either they left before they even know we existed (we didn't have any emissions that indicated intelligence, though they might be able to detect life), and so they are not equipped to deal with us. If they want to take over - they didn't break enough weapons because they didn't expect to need them.
Even if life is common in the universe, it isn't common in any area where an intelligent civilization can expect to actually reach without FTL.
Alpha Centauri is just 4.37ly away. With an acceleration of 0.00227g, mass of 1t, and max velocity of 0.1C (10% of C), it will take 86.33 years to reach Alpha Centauri for those on the spaceship, assuming you also want to stop at the destination. (Calculator: https://www.omnicalculator.com/physics/space-travel#space-tr...)